My Dell PC, which is an older model running Windows XP, is very slow to boot up and I have a lot of icons on my desktop. Does the number of icons on my desktop have any relationship to the time it takes my PC to boot up?

Everything a PC must do when it starts up takes some time, and that includes drawing the desktop. A desktop with fewer icons takes less time to re-create. But, if your machine is “very slow” to start up, you may also have accumulated too many programs that are set to run upon start-up, including programs that you can’t see because they are launching behind the scenes. So, it would be wise to examine these programs and remove or disable as many as you can, keeping only those you really need. I suggest you obtain and run a program designed to help you do this. One good one comes from PC Magazine and is called Startup Cop Pro 3. It costs $8 and can be found at pcmag.com/downloads.

If I buy a Mac, can I move all the programs on my Dell over to the Mac?

While most common Windows file types can be copied to a Mac and will work there, the Windows programs on your Dell won’t run on the Mac’s operating system, so there’s no point in moving them to a Mac. There is one exception: If you plan to install and use Windows on your Mac, then your programs should run. However, some programs are designed to be locked to a single PC and won’t run on a second machine, even if it is a new Dell instead of a Mac running Windows. Furthermore, it can be difficult to move Windows programs to a new machine, because they are often made up of parts that are scattered in various places on the hard disk.

Two of the companies whose software allows you to run Windows on a Mac, Parallels and VMWare, do offer utilities that will copy the contents of a Windows PC to the portion of the Mac devoted to running Windows. The Parallels utility is called Transporter and the VMWare utility is called Converter.

Like many Internet users I have used Wi-Fi in airports, hotels and coffee bars. I have used it to access banking and brokerage accounts. Just how much at risk have I been? I am a Mac user. Am I more or less at risk than a Windows user?

No matter what kind of computer you use, there is some chance, however small, that a crook can intercept any data you send or receive over a public wireless network. So, my advice is to never, ever conduct financial transactions, or any highly sensitive communications, over any network you don’t control. It’s the same principle people should use when making voice calls on cellphones, which are easier to intercept than voice calls made on land lines. Be cognizant of the content of your communications of any kind when you are using public wireless networks.

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

Here are a few questions about computers I’ve received recently from people like you, and my answers. I have edited and restated the questions a bit, for readability. This week my mailbox contained questions about recovering deleted icons, clearing search histories and the difference between laptop processors.

If you have a question, send it to me at mossberg@wsj.com, and I may select it to be answered here in Mossberg’s Mailbox.

I accidentally deleted from my Windows XP desktop the icon for a program I use often. I know that this doesn’t mean I have deleted the program. But how do I get its icon back on the desktop?

There are multiple ways to do it, but here are a couple. You can click on the Start Button, then on All Programs, then locate the entry for the program, and just drag that entry onto your desktop. Or, you can locate the program file itself (it’s typically in a subfolder of the Program Files folder), select the file, click the right mouse button and then click on “Send To.” From the next menu that appears, select “Desktop (create shortcut).”

In the Firefox Web browser, how do I erase all traces of my browsing activity, so another user of the same computer can’t see what I’ve been doing online?

Go to the Tools menu, and select “Clear Private Data…”. This will bring up a list of traces that can be expunged. You just check off the ones you want obliterated, and then click on the button at the bottom labeled “Clear Private Data Now.”

To be absolutely safe, you can check off the entire list, but, generally speaking, clearing the browser history, download history, cookies and cache should hide your tracks from a casual user.

Be aware that there’s a downside to this. After clearing out this stuff, your Web surfing could slow down a little, because you won’t have any cached pages for the browser to use to speed up the loading of sites you’ve visited in the past. Also, by purging all cookies, you will lose the automatic log-ins and saved preferences, from some sites.

I am shopping for a laptop, and am confused by some of the processor choices. Specifically, what is the difference between Intel’s new Core Duo chip and the Core Solo chip?

Both are new designs, which combine power with greater efficiency. They run cooler than older processors, thus allowing for thinner laptops, fewer fans, and, in some cases, better battery life. But the Core Solo is, like most past processors, a single digital brain. The Core Duo packs two brains — two “cores,” each the equivalent of a single processor — onto one chip. This potentially offers greater speed in performing tasks on the computer, especially when you are running several programs at once, and especially if one or more of the programs is demanding.

Bear in mind, however, that to get the most out of the dual-core design, your software should know how to use the twin cores. Not all software does, though this should improve over time, as software is revised to better use the new chips. Also, the overall performance of a computer depends on many factors beyond the processor. These include how much memory you have, the power of the video subsystem and the speed of your Internet connection.

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Because of the volume of e-mail I receive, I can’t routinely answer individual questions by e-mail, or consult on individual problems or purchasing decisions. I read all questions I receive and select three each week to answer in the column.

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