detecting OS win2k

Hi,
I need to determine if a user is on windows 2000 Professional before writing to a page. In the userAgent string I see that my OS (win2k) shows up as

windows NT 5.0

So can I search the string for 'NT 5.0' and be assured that I'm always dealing with win2k? Or do some variations of 2k return a different string... or for that matter what do other windows verisons return... NT, ME, XP etc.

If you want to help me out you can pop this into your location bar and share the results:
javascript:alert(navigator.userAgent);

Or if anyone has done this same thing before would be even better.

Thanks a lot for any insight.

There's a great sniffer over at www.docjs.com