Kathy Sierra's most recent blog post [headrush.typepad.com] deals with the perennial favorite topic in forum 103. I can boil it down to one line: "get non-expert members to answer questions, and don't allow rudeness."
I think it's an interesting complement to martinibuster's thread about authoritiative answers [webmasterworld.com] (rightfully in the library, cheers) as the enemy of discussion. mb's post suggests that you draw out lurkers by avoiding definitive answers. KS's post sort of comes at the same idea from a different direction, which is to get answers from people who wouldn't consider themselves experts.
Mix these together, shake over ice, strain into a glass and serve with appropriate garnish and you may have something...
I think it's a fairly natural progression for new members to be mostly askers of questions. Over time, they will gain posting confidence and will probably increase their knowledge level. In addition, they will start to feel they are part of the community and will be anxious to give something back when they are able.
For the member ASKING the question, the best response is one that is quick and authoritative. Quick help will bring these (often new) members back with more questions, and eventually they will be part of the answer cycle, too.