You are the victim of spyware/adware (which is collectively known as malware), at least one homepage hijacker, and probably a few viruses. First, read this article to acquaint yourself with the problem:
http://www.bleepingcomputer.com/tutorials/tutorial41.html Next, run Ad-Aware. What's Ad-Aware? Please read this thoroughly:
http://www.bleepingcomputer.com/tutorials/tutorial48.htmlThen run SpyBot. What's SpyBot? Please read this thoroughly:
http://www.bleepingcomputer.com/tutorials/tutorial43.html Note: I've had to run SpyBot several times in a row to completely remove some of the more stubborn varieties of malware. Also, remember to immunize your computer. Read the article and you'll understand.
Now run HijackThis. What's Hijack this? Please read this thoroughly:
http://www.bleepingcomputer.com/tutorials/tutorial42.html Note: It is possible to do significant damage to your computer with HiJack This! Because of this, when you create a log file (Read the article and you will understand what a log file is) post it as an attachment to this message board. We'll help you through it. Also, the above article is rather lengthy. You really don't need to read it all, just the first five "chapters".
Next run Panda Software's free online virus scan:
http://www.pandasoftware.com/products/activescanpro/ Note: The link for the free scan is rather hard to see. Its in the upper right corner just underneath the red rectangle that says "Buy ActiveScan Pro". The link says "Free Online Virus Scan". Click the word "Online". It *REQUIRES* Internet Explorer 5.0 or higher to run. It supposedly removes any viruses it finds, but you need to upgrade to the Pro version to remove spyware/adware. Don't worry, Ad-Aware, SpyBot, and HiJack This do just fine (and their free!!).
Then, just for good measure, run Ad-Aware and Spybot once more.
Finally, Get Spyware Blaster. What's SpywareBlaster? Please read this thoroughly:
http://www.bleepingcomputer.com/tutorials/tutorial49.htmlIf you really want to be thorough, use SpywareGuard. What's... Okay I'll stop. Just read this:
http://www.bleepingcomputer.com/tutorials/tutorial50.html Note: I've never used it myself, but it looks like a good idea.
You've got enough tasks ahead of you to burn through a few evenings.
Keep us up to date with your progress.
--Oober Noober