[Irishsquid]

Sounds almost like a "Man in the Middle," attack, or DNS poisoning. Check your SSL certificates...make sure they are valid, not expired, and issued by a reputable CA...and that they are the CORRECT certificates for the site you are trying to hit.

Also, try running a "netstat -a," from the DOS prompt. That'll show you all your open connections. Look for connections to an unfamiliar IP address, or for listening ports that shouldn't be listening. That can be a big clue for malware on your system.