First eliminate any scumware.
See
Dealing with Unwanted Malware, Parasites, Toolbars and Search Engines
http://mvps.org/winhelp2002/unwanted.htm

Note that AdAware and SpyBot S & D will each catch some things the other
won't.  Also, each needs to be updated with the program's update function
before every use, even when just downloaded.  There's also a lot more to do
than just those two programs.  CWShredder is also available here:
http://www.kellys-korner-xp.com/regs_edits/cwshredder.zip
**Post your HijackThis log to
http://forums.spywareinfo.com/ or the Spyware forum at
http://forum.aumha.org/ for expert analysis, not here.**
Alternative download pages for Ad-Aware, Spybot, HijackThis and CWShredder
may be found on this page:
http://aumha.org/a/parasite.htm.

If nothing there helps, please post back to this thread.