Both are fine, although we see Unix more frequently. 3rd party FTP for NT is desirable. Unix's sendmail is more frequently used. POP and IMAP clients are available for each. Bugtraq and NTbugtraq are full-disclosure lists where announcements about new security expolits and workarounds are posted.
Many resources are out of date, and none are authoritative.
Microsoft's security pages , includes link to NT pages. Aelita Software Group includes Security Checkbox, a tool for automatically checking your NT security. The Orange Book specifies levels of security and their criteria. Get help Laws United States House Virtual Law Library , includes links to states with laws online North Carolina General Statutes and General Assembly information. Many hacking channels and discussion.