Sounds like you picked up a hijacher. you need to run an antispyware program
like Ad-aware to get rid of it. ad-aware is a free download and works great.
Spybot 1.2 works good to. after you get rid of it download spyblaster 3.1
run the update and it will keep that kind of junk from getting on your pc.
It works with internet explorer to stop them before they get in.
It is also a great program and is free.
I forgot to mention runing the updates for ad-aware and spybot first
before you actualy run the programs.