If you have an active subscription to an antivirus program, make sure that it is up to date. If your subscription is over either renew it or use RevoUninstaller to uninstall it. Then install AVG in its place (Remember, you should only have ONE antivirus program installed on your computer). Regardless of which of these you do, then install ThreatFire.
You should also visit the Google Pack website in order to download Spyware Doctor for free.
I would also recommend that you use Mozilla's Firefox instead of Internet Explorer. Once it's installed, you should also install the Adblock Plus add-on. After it's been installed, it will ask you if you want to add certain premade lists. I find that instead of adding one, it's best to visit the homepage of EasyList, and add all three lists from there, instead of just one from the original menu.
If you don't already have a firewall, I would strongly recommend that you download Comodo. It can be a bit annoying to "train" it, so when it asks you questions, answer truthfully and thoughtfully.
These programs should get you well on your way, and might even possibly fix the problem on their own. If they don't, or if you're interested on how to protect your computer further, feel free to check out my step by step guide on malware removal. It includes the programs I just mentioned, a few more, and their optimal settings. You can find it here: http://prometechus.blogspot.com/2007/09/viruses-spyware.html
Best of luck, hope this helps. Also, don't forget to check if anyone has asked a similar question before asking one yourself.