You cant remove Windows XP. Fix the problem.
Download the programs linked below. Install them. Update them. Scan your pc with them, and do so weekly.
If you have System Restore turned on, the Restore files may be infected, and trying to reinfect your pc. I turn off that feature, reboot to delete the files, then turn it on after a full system scan with AVG.
Turning off System Restore.
(right-click My Computer, Properties, System Restore tab, check the box to turn off System Restore on all drives.)
Restart your PC, and hold down the F8 key.
When you see the Boot Menu appear (black screen white letters), choose SAFE MODE.
Run a FULL SYSTEM SCAN with AVG.
You can heal or quarentine anything found.
You can also run Spybot and AdAware while in Safe Mode. I suggest you do a full system scan. Get rid of anything they find.
To exit Safe Mode, just restart your PC normally.
AVG Antivirus - Free Antivirus Software
(CNET: "AVG Anti-Virus Free Edition is the most popular free solution available at no cost to home users and provides the high level of detection capability that millions of users around the world trust to protect their computers.")
Ad-Aware - Free Antispyware Software
(CNET: "One of the first applications built to find and remove adware and spyware, Ad-Aware 2007's excellent reputation is well-justified.")
Spybot Search&Destroy - Free Antispyware/Antitrojan Software
Some REALLY great features of Spybot Search&Destroy: Its ability to help your PC block known spyware/hijacker sites with Immunize feature, a Secure Shredder for truly removing files from your PC, and Startup, which allows you to view the files starting with Windows.
SuperAntiSpyware
SUPERAntiSpyware Free Edition is 100% Free and will detect and remove thousands of Spyware, Adware, Malware, Trojans, KeyLoggers, Dialers, Hi-Jackers, and Worms. SUPERAntiSpyware features many unique and powerful technologies and removes spyware threats that other applications fail to remove.
Hope this helps.