critical system error message about trojan infection

A window keeps popping up telling me I am infected by a trojan and it wants me to download a removal tool, which turns out to be IE Defender. I gather that my IE was hijacked to go to a fake site disguised as a Microsoft/sympatico site. If you aren't aware, Microsoft Canada and Bell Sympatico went partners a couple of years ago. My original home page was www.bourque.org, a Canadian news site. On the fake site I was shown an add to download a program to optimize IE7 for use with sympatico. So I figured why not. Big mistake. After that the pop-ups started and I ended up downloading IE Defender. I uninstalled IE defender but can't get rid of the pop-ups. I guess they want you to buy the program which stop the pop-ups. I have tried almost everything, even from a thread on this site dealing with the same problem, except I'm using Windows Vista, so some of the things to be tried from that post don't work on here. Funny thing is I never use IE. I am a Firefox user. I don't know what made me open IE in the first place. And the pop-ups only occur from within windows, meaning when I open IE or anything related to windows explorer, It never happens when I open firefox or any programs.

 

Well that seemed to do the trick. Thanks for replying so promptly.:cool