I recall that one, or both, of these free Microsoft tools has an option to return your copy of Internet Explorer to its original factory settings:
Microsoft Baseline Security Analyzer:Microsoft Anti-Spyware (Beta) The second tool installs itself as a startup utility, and runs periodically to check for spyware, so make sure that that's what you want. The current versions of both of these tools may also require that you do Microsoft's confirmation that you have a licensed copy of XP, so make sure that you're comfortable with that, also.
I recall you mentioning using Spybot Search and Destroy, so I'll assume you have run the current version already (in Windows "Safe Mode" and from read-only media if you want to be absolutely sure).
Paul W. Schleck email@example.com@novia.net for PGP Public Key