Welcome to the wonderful world of spyware! Believe it or not, you've been hit by the more benign type of spyware, and there's much worse awaiting you out there.
The first step, is to download a copy of AdAware and Spybot. Update the both of them after installing, then run the both of them twice. Once before, and once after, rebooting. That should clear up most of the garbage currently installed.
Step two, is preventing the spyware from being installed again. This requires that you stop using Internet Explorer, because it is one of the primary targets for spyware makers. It's so littered with security holes, that these things can be installed on your system without any sort of notice being give to you.
So, you need an alternative browser, which isn't just a different front end to IE. Which leaves you with three options on Windows: Mozilla, Firefox, and Opera. The first two are completely free, Opera is free with a constant ad banner in the browser, but the registration cost is reasonable IMO. Try all three, keep all three, or just the one you like best. Just don't use IE for anything other than twice monthly visits to the Windows Update site to make sure you've got the latest crittical updates installed.