Microsoft's Knowledge Base (Rate)

Can be used to search for answers to Windows questions.

MCSE Directory (Rate)

Contains free study guides, practice exams, additional study resources, free IT books, networking information, and more. Named by Windows 2000 Magazine as "Certification Web Site Gold Mine".

John Savill's NT/2000 FAQ (Rate)

An excellent site with documentation and answers to frequently asked questions about Windows NT and 2000.

VirtualDr (Rate)

Has answers to questions about many platforms.