I bought an iPhone and was frustrated that my fingers appear to be too large to type properly on its virtual keyboard. Is there a stylus that works with the iPhone?

I hadn’t realized this until recently, when a friend who bought one showed it to me, but, yes, there is. The iPhone wasn’t designed to operate with a stylus, and the small, thin, hard kind that one uses with, say, a Treo, doesn’t work right with the iPhone. But there are some companies that sell a wider type of stylus with a soft tip that approximates a small fingertip, and is designed for the iPhone.

If you type “iPhone stylus” into a search engine, or an online store like Amazon.com, you will see a number of inexpensive choices. One downside: the iPhone doesn’t have a built-in slot for a stylus. My friend carries his, which has a clip on the end, like a pen, in his pocket.

I just purchased an external hard drive for my PC that connects through a USB port to back up photos and important files in the event of a computer crash. Would this hard drive be affected if my main hard drive crashed? Should I disconnect the external drive when it’s not in use?

The two hard disks are separate devices, and if one has a mechanical failure, it doesn’t affect the other. There might be some scenarios in which a problem with the computer itself, as opposed to a breakdown of its internal hard disk, could affect the external drive. And malicious software could corrupt or erase files on the external drive. An electrical surge could also affect both drives, or fry the computer itself.

Many people can’t disconnect their external drives, because they use automated backup programs, or frequently save files to the drives. If you are doing only occasional manual backups, you could disconnect the extra drive when not in use, so you’d feel more comfortable. But, for maximum peace of mind in case of an electrical surge, you should disconnect it not only from the PC, but from the electrical outlet as well, even if you are using a surge protector.

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

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

After reading your positive review, I downloaded Firefox 3.0, only to discover that some of my favorite add-ons, including a search toolbar, are incompatible. What can I do about this?

Wait. As I noted in the review, when major new versions of Firefox come out, it takes a while for some of the many add-ons for the browser to be updated so they are compatible with the new version. Because these are written by a very large number of different companies and individuals, the process will be gradual, and some will be updated more quickly than others.

As for search toolbars, like those from Google (GOOG) and Yahoo (YHOO), I doubt that most people still need them. When they first came out, these toolbars provided things the top browsers lacked: a permanent search box, pop-up blocking and a few other useful features. But all the major browsers now provide these things without requiring the installation of any external toolbar. The companies that make the toolbars can use them to sell advertising or attract you to their search engines. But, for many users today, they are redundant.

I don’t want to run antivirus software constantly, but I would like to periodically run a program that could scan my computer and remove viruses and the like. Does such a program exist?

Yes. Here’s one example. Microsoft (MSFT) makes a small, free program called the Malicious Software Removal Tool that looks for, and tries to remove, a limited number of the worst examples of malicious software. It can be downloaded at www.microsoft.com/security/malwareremove.

However, this isn’t a comprehensive antivirus program. Microsoft says it detects and removes only “specific, prevalent malicious software,” and advises that “You should also use up-to-date antivirus software to help protect your computer from other malicious software.”

I am in the market for a laptop. I was considering a Dell (DELL) or an H-P (HPQ) but have learned that Apples now run Windows. I have financial (Quicken) and other business files (Excel, Word and PowerPoint) that would need to be transferred to the new computer. Would this be possible on an Apple (AAPL)?

Yes, in the same ways you could transfer files from one Windows PC to another. For example, you could burn them to a CD or DVD, copy them to an external USB drive, or transfer them over a network or via the Internet. In fact, if you buy your Mac at an Apple retail store, the store’s staff will move your files over free, or for a modest fee, depending on which folders, and how many, you want transferred.

Once the files are on the Mac, you can either use native Mac programs to read and/or modify them, or you can install Windows and run your usual Windows programs to handle the files.

For instance, even if you never installed Windows on an Apple, your Excel, Word and PowerPoint files could be used in the Mac version of Microsoft Office. However, the Mac version of Quicken isn’t as compatible with the Windows version’s files. So, for Quicken, I suggest installing Windows on the Mac and running the Windows version of Quicken.

• 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.