Should I install Microsoft’s “SP3″ upgrade to Windows XP? I hear opinions on both sides.

In general, I recommend this upgrade, officially called Service Pack 3, because it beefs up security, and that helps not only you, but all Windows users, to avoid the spread of malicious software. If your PC is more secure, it is less likely to be used as a source from which other PCs can be infected.

I have upgraded a couple of XP PCs to SP3 without any downside. However, like you, I have also heard from some users that the upgrade caused them problems.

As with any major operating-system upgrade, either outcome can occur, depending upon your computer’s particular configuration and condition. So, if you’re on the fence, consider your level of concern about security.

How do cellular data cards compare with fast cable modems in terms of Internet speed? Are these cards more secure than Wi-Fi?

In my experience, using and testing cellular data cards on various laptops, they typically deliver, in real day-to-day use, somewhere between 300 kilobits per second and 1.5 megabits per second. By contrast, a fast cable Internet service can actually deliver up to 16 mbps. So cable is much faster.

Your security question is much more complicated. Wi-Fi security can range from very poor to quite good. It depends on where and how you use Wi-Fi, how you or others have set up the wireless network, and how you have configured your own computer.

Accessing the Internet over a cellular network is a more controlled process, because the cellphone-network operator manages the transmission, and in most cases supplies and configures the software on your computer. So, it is likely to be safer than the worst Wi-Fi setups. But I would never suggest that cellular data card transmissions are invulnerable to hackers or criminals.

What’s the difference between file-based backup and image-based backup software? Why would I choose one over the other?

Image-based backup software copies an image of your entire hard-disk, including all the programs, settings and obscure files that you never see. While it can be used to recover individual files, in some cases, it is mainly designed to allow you to restore your entire hard disk in the event that you lose it all.

File-based backup software, which is more common among consumers, is typically designed to preserve a copy of only your personal data, the material you can’t re-purchase or re-install if your hard disk dies.

That includes word-processing files, spreadsheets, presentations, emails, contacts, calendar items, photos and other items you created. It also is often used to back up music and video files that would be time-consuming, or very expensive, to re-acquire. And in some cases, it can preserve settings and preferences, such as Web bookmarks.

Both types of backup generally begin with a time-consuming initial session, followed by shorter sessions to update the backup with incremental changes.

Many people choose file-based backup because it occupies less space, and is generally quicker and also less expensive. Image-based backup is for folks who are willing to spend the added money and time to be sure they can restore their whole computer, or clone its contents completely to another machine.

• You can find Mossberg’s Mailbox, and my other columns, online free of charge at the new All Things Digital Web site, http://walt.allthingsd.com.

My computer takes forever to start up. I am tempted to just put it into hibernation or standby when I am done with it for the day, so that starting up will be quicker. Would I be damaging my computer by doing so?

Doing this shouldn’t cause any damage to your computer. For many users, one of these two techniques is standard procedure, in fact. Standby, or sleep, mode, gets you back to work more quickly, because the machine never completely shuts down. Its biggest downside is that, on occasion, computers fail to “awaken” properly from this mode, and you have to do a full restart. So I would advise that you carefully save any work before initiating standby.

In my experience, this kind of glitch is less likely to happen when you use hibernation, in which the computer does completely shut down, but first saves to the hard disk a record of the state of the machine.

When the computer restarts, all open programs and files are restored just as you left them. The downside here is that getting going again using hibernation takes longer than it does using standby mode. And, even though it’s more reliable than standby mode, I’d still advise saving all your work each time before using hibernation.

I am thinking about switching to a MacBook Pro laptop. I understand that it has a real good automatic Wi-Fi detection system. But if I also use a cellular modem card from Verizon or Sprint to access the Internet, won’t the two conflict?

No. The Mac operating system treats the two kinds of connections separately, each with its own user interface. It can detect and connect either one, if you have coverage of both types.

I’m interested in getting a laptop with LED display and SSD drive. Do you think the price for those components will fall drastically in three months’ time?

Displays that use light-emitting diodes (LEDs) have been around for a while and don’t tend to be a major deal breaker in the higher-end laptops in which they are commonly offered. But solid-state drives (SSDs), which replace hard disks with memory chips to store your data, are much rarer and newer and still can add significantly to the price of even a high-end laptop. I am no expert in price forecasting, but, while SSD prices will fall, I doubt they will drop “drastically” in as little as three months.

You can find Mossberg’s Mailbox, and my other columns, online for free at the new All Things Digital web site, http://walt.allthingsd.com.

With the new iPods coming out, how do you deactivate an old one? I think Apple only allows a certain number to be used with an account.

You don’t have to deactivate an iPod if you replace it. The copy-protection rules imposed on Apple by the entertainment companies allow for copy-protected music and videos purchased from the iTunes Music Store to be stored and played on an unlimited number of iPods.

The only “deactivation” iTunes users have to perform is on a computer — Windows or Mac — because the copy-protection rules allow purchased, copy-protected songs and videos to be played on no more than five computers at a time. So, before you replace a computer on which you are storing such purchased, protected iTunes material, you should deauthorize the machine by going to the “Store” menu in iTunes and selecting “Deauthorize Computer…”.

Of course, if you aren’t at or near the five-computer limit, this issue may not matter. It’s also irrelevant if none of the music or videos you play from within iTunes is copy-protected material purchased from the iTunes store. You can happily use iTunes and iPods without buying any copy-protected stuff from Apple. You can restrict your music and videos to those you copy from legally obtained CDs, those you create yourself, or those you buy in unprotected formats from iTunes, or other sites, like eMusic.

I have a printer hard-wired to a desktop computer, but would like it to be available to my laptop wirelessly over my home network. How can I do this?

There are two main methods, assuming the printer doesn’t have a built-in networking port or Wi-Fi transmitter. One method is to buy a small box called a print server and plug it into your router. Then, you plug the printer into the print server, and, with the right software and settings, it will appear on your network and be available to any computer on the network, wired or wireless.

The same companies that make routers, such as Linksys and Belkin, also often make these print servers. The other method is to buy a wireless router that has such a print-server function built-in, with a USB port for connecting a printer.

If I have a laptop with Wi-Fi capability, does that mean I can surf the Web while sitting in a car?

Yes, but only if the car is in range of a Wi-Fi network that is either open (not password-protected) or for which you know the password. And it would only be practical if the car was stopped or parked, since a car moving at normal speed would very quickly drive out of range of any networks you encountered.

A better option, which works even when a car is moving, is to purchase a high-speed cellular wireless modem for your laptop, or buy a laptop with such a modem built-in. These modems, which get you on the Internet via citywide cellular-data networks instead of Wi-Fi, can remain in range for miles. But they require hefty fees, typically $60 a month. And, of course, you should only be surfing the net in a moving car if you are a passenger in that car, not the driver.

You can find Mossberg’s Mailbox, and my other columns, online for free at the new All Things Digital Web site, http://walt.allthingsd.com.

Write to Walter S. Mossberg at mossberg@wsj.com