Boot in Safe Mode then check your system for "hijackware".

Dealing with Hijackware
http://mvps.org/winhelp2002/unwanted.htm
http://www.mvps.org/inetexplorer/Darnit.htm#tshoot
http://aumha.org/a/parasite.htm

HijackThis (http://www.spywareinfo.com/~merijn/files/hijackthis.zip) is the
preferred tool to use these days.  It will help to both identify and remove
any hijackware/spyware.  **Post your files to
http://forums.spywareinfo.com/, not here.**

Also update your virus definitions and then run a full system scan.  From
now on, do both daily.

Post future questions to this IE6-specific newsgroup:

news://msnews.microsoft.com/microsoft.public.windows.inetexplorer.ie6.browser

HTH...Please post back to this thread

~Robear Dyer (aka PA Bear)
MS MVP-Windows (IE/OE), AH-VSOP

Protect Your PC
http://www.microsoft.com/security/protect/default.asp