Ken,
Do you have a direct link from you frontpage to your forum? If you do pr from the index page sould pass to the forum

I'm not really sure temi as clicking on the forums brings it up as a module: modules.php?name=Forums. Is this the problem?

The type of link could be the problem, but another thing to look at first is links back to the home page from within the Forum php pages.

If you don’t have a link (preferably a Text Link) back from inside the forum pages to the Home Page, then Google will treat the whole Forum as a “Blind Alley or Cul-de-Sac. This link should be in the "Header" or "Footer" ensuring its presence on every page.

You might also consider a stand alone structure of Home Page plus a descriptive page for EACH of the primary "Search Phrases" that you wish to be found for. Each of these pages should link to each other and the Home Page plus of course link into your Forum. Try to keep this group of pages down to single figures if you can.

essentially what you are looking to do is trap your pr on your site without leaking it to other sites, or just keeping the pr on your index page. what i would recommend is to create a site map which is linked to from your index page. once you have built a site map this should help to start spreading pr to all the pages. to keep the pr from leaking out to other sites try to make sure that you have a nice internal linking structure. in addition adding a footer at the bottom of your page is a nice way to trap googlebot on your site encouraging it to spider more pages, and keep the pr within your site.