QIs the choice between the Intel Pentium 4 and AMD Athlon XP processors really going to make that much difference?

ANot in terms of compatibility -- both handle the same Windows programs. Pentium 4 and Athlon chips do run at varying speeds, but the way they're labeled makes it hard to tell which ones are faster.

For years, Intel sold its chips by clock speed, as measured in megahertz and now gigahertz. A few years ago, however, AMD developed its own speed rating: For example, its Athlon XP 3200 runs at 2 GHz but, AMD says, performs as fast overall as a 3.2 GHz Pentium 4.

Intel's next set of chips, however, will be identified by their processor family, then a three-digit number indicating relative speed (say, "Pentium M 735"). Hmm . . . still confusing, since Intel and Athlon don't calculate these performance ratings in the same way.

To settle the issue, sites such as AnandTech (www.anandtech.com) and Tom's Hardware Guide (www.tomshardware.com) run extensive benchmark tests. But for most home use, any P4 or Athlon XP is more than fast enough.

I got hit by the Sasser worm, and now my machine keeps shutting down before I can finish downloading Microsoft's patches.

Our reader forgot to enable the firewall in Windows XP before getting Microsoft's updates. As a result, the Sasser worm continued to attack the computer, forcing a restart.

You can abort that restart by typing "shutdown/a" in the Start Menu's "Run . . ." dialog box; enter this command ahead of time, then click the Run box's "OK" button when the shutdown sequence actually starts.

But you can prevent it entirely by enabling Windows' built-in firewall: Open the Network Connections control panel, right-click on your connection's icon, select Properties, then click on the Advanced tab.

-- John Gilroy

John Gilroy of Item Inc. is heard on WAMU's "The Computer Guys" at noon on the first Tuesday of the month. Send your questions to him in care of The Washington Post, 1150 15th St. NW, Washington, D.C. 20071 or via e-mail to jgilroy@iteminc.com.