Obviously if you generate a sitemap for your forum you will have thousands of pages of junk. Do i make a sitemap with just the main forums included? Thanks for the info!
If you want google to index all your pages, you make a sitemap for the whole site, or just make a sitemap for the main forums. But I don't think you can stop google from indexing your pages in the case that you have inbound links for your pages.
I totally agree with hhheng, and why shouldn't you want that google indexes all your pages? The more pages google will index for you the better I guess.
For XML sitemaps, you should include all pages. For HTML sitemaps, only the main entry points to the forum.
In my XML sitemap i include the forum categories, thread pages, and member profile pages. search, members list, contact, faq, register and show post pages don't have any real content so i just exclude them with robots.txt and don't include them in the sitemap.