This is known in the trade as a browser hijack.
http://www.spywareinfo.com/~merijn has cwshredder, which
may well solve the problem.
However, it is likely that you will have other
adware/spyware/crapware on your pc as well, so I would
recommend a couple of additional things:
http://www.ad-aware.com - ad aware
http://security.kolla.de - Spybot S&D
Download, install, update, and run ad aware, reboot, then
do Spybot the same.
If you continue to have problems, go back to Merijn's
homepage, get hijackthis, and go to the spywareinfo.org
forums and read the FAQs and then register and post your
hijackthis log. Everything you need to know that I've
kind of skimmed over is at the forums, or available at
one of the links I included.
Good luck
Derrill
