What is a listserv?
http://en.wikipedia.org/wiki/Listserve
NTSecurity.Net Win2k Security Advice
This site offers tons of NT how to advice and all the latest security news.
NTBugTraq Listserve
With over 30,000 subscribers, this list is an excellent resource for anyone who needs to keep track of the latest security holes and fixes available for their NT server.
SecurityFocus.com's MS focus list
http://securityfocus.com/archive/88