I know for a fact that many, many people have problems with their browser – pop ups, ads, and just general clutter that ends up in (typically) Internet Explorer.
This article describes (in detail) some steps to remove all the junk, extra toolbars, and strange start-up pages that you may have.
http://bcheck.scanit.be/bcheck/hijacked.php
I have personally reviewed the article, and found it to be technically correct, so you can feel safe following the instructions contained therein.