Give this a try goto the Microsoft update page and follow the
link and choose the operating system as NT and it will allow you to download a free version for 12 months. I donââ‚Âà ‚¬ÃƒÂ¢Ã¢â‚¬Å¾Ã‚¢t know if it will run as a service as I am installing at the moment. It has just started to perform a virus scan, so itâ₠¬ÃƒÂ¢Ã¢â‚¬Å¾Ã‚¢s looking good.
Funny thing is it donââ‚Âà ‚¬ÃƒÂ¢Ã¢â‚¬Å¾Ã‚¢t show if you are using XP I was updating a ME puter and saw the link.
Edit: Well it looks like a good one, it loaded ok on Windows 2000 advanced server, done a check and re-started. Not bad for free