Your browser has been Hijacked by spyware or a Broswer Helper Object
(BHO). Download these 2 products, install them, UPDATE THEM, then run a
scan and have them remove ALL the parasites that they find.
AdAware:
http://www.lavasoftusa.com/software/adaware/
Spybot Search&Destroy:
http://www.safer-networking.org/
Don't forget to look for updates before running the scan, there is
update features right in the programs. After you run these programs you
may still have BHO's and spyware, some can be pretty tenacious and need
special tools to remove, CoolWeb for example. Post back if you still
have problems.
John