My first reaction would be to say that it sounds like you have a spyware issue - perhaps a browser hijack attempt that wasn't written so well by the attacker. Try running your virus scan - a full scan while you're in Windows Safe Mode. If it doesn't solve the problem, download, run, update, and scan with "Ad-Aware" - a free program by Lavasoft most easily available from download.com that scans specifically for non-virus malicious programs ("malware") on your computer. You might also want to try Webroot's SpySweeper, although AdAware, in my experience, works better if you compare the free editions of both applications. If you're willing to pay, SpySweeper is more effective, but AdAware generally gets the job done without costing you a cent.