Recovering from a very deep infection is not easy… maybe starting all over again, from the scratch, will be easier than trying to fix them…
Anyway, maybe overinstallation can solve the problem and you won’t lose your programs, settings, data, files, etc.
Just choose ‘Repair’ installation of Windows and install ‘over’ the old installation.
http://support.microsoft.com/default.aspx?scid=kb;EN-US;315341
http://support.microsoft.com/default.aspx?scid=kb;en-us;Q314058
http://www.webtree.ca/windowsxp/repair_xp.htm