These are covered in the existing SharePoint - Development and Programming forum. (As all web part development requires programming)
It's possible that there may be a forum reorganisation (of the SharePoint forums) when SharePoint 2010 is released (or maybe even when it goes into public beta) but I think this is more likely to be a change to the specification of what is covered in the existing forums (the PerformancePoint features that have been publically said will be moved into SP 2010 will need to go somewhere - probably the existing BI forum) rather than the addition of new forums.
The only exception I can see to this is if SP 2010 includes some totally new function (in the way that MOSS 2007 included Excel Services) in which case I would imagine a new forum would be created for it by the team behind it. But I can't remember seeing anything in the three sneak videos that would indicate such a radically new function.
WSS FAQ sites:
http://wssv2faq.mindsharp.com and
http://wssv3faq.mindsharp.com Total list of WSS 3.0 / MOSS 2007 Books (including foreign language)
http://wssv3faq.mindsharp.com/Lists/v3%20WSS%20FAQ/V%20Books.aspx
