As far as web-based forums go:

Two "biggies" out there are debianHELP and the Debian forum at LinuxQuestions.org. These are high-volume boards and one has a tendency to get lost in the shuffle, but they're good for searching for answers.

This forum (Knoppix.net) is probably acceptable for posting Debian-related questions, especially after you've installed Knoppix! Another good forum that's lower-volume, although it's not specifically Debian-related, is at LinuxFormat's web site. (Linux Format is a British magazine with a great "cover CD" that you can buy at many Barnes & Noble's in the US.)

(I haven't tried looking to Usenet newsgroups for help with Debian yet.)