If you're re-setting-up WinXP, then start WinXP Setup from CD-ROM, get to where it shows the drive partitions, delete them all, then hit F3 twice to exit Windows Setup. Now start WinXP Setup from CD-ROM again, create partitions and carry on.
This keeps your boot process from having a screen showing two instances of WinXP to choose from. Bigger picture: to help with your CWS problem,
1) firewall(s)
2) up-to-date, current-model antivirus software fully configured to play hardball (all options, all files, all the time, no asking the user what to do). Keep it updated. Any more, I would update daily if the vendor has that option (Symantec's daily Intelligent Updaters for example).
3) keep up-to-date on your Microsoft patching, and run Microsoft Baseline Security Analyzer to help with some stuff Windows Update won't help you with.
4) use a Limited account for your daily-driver activities, it lacks the power to install junk (and that applies to anything trying to subvert the Limited account's powers, too)
5) give all your system's Administrator-class accounts strong passwords such as sonambulo@AT for example.
6) do not be a stupid-head. No warez, pr0n, or other stuff you don't know where it really comes from, that would make a logical vehicle for malware.
edit: one more thing, personally I leave System Restore disabled. It usually has to be disabled to remove viruses anyway, not that I'm having any firsthand experience with that 😛
