sounds like spyware. that's what you get for continuing to use internet explorer. Once the problem is solved I suggest you switch to firefox.
Grab:
- HijackThis
- AdAware Personal
- SpyBot search and Destroy
use HJT,
http://www.spychecker.com/program/hijackthis.html, and head on over to
http://computercops.biz/forum67.html with your report (or any mainly antispyware forum with a hijackthis forum)
Run AdAware and download the latest update. Run under normal settings, fix as needed.
Run Spybot and download the latest update. Run under normal settings, fix as needed.
reboot into safe mode and repeat the last two steps.