Hey, I love this idea, but I think you need content first, forums second.
I'd like to say that most communities don't start with forums, but with information. If you built a page that gave lots of good links, divided into sub categories, you'd have a lot more interested people. For example -
www.mp3car.com - build your own mp3 system for your car
www.hometheaterforums.comwww.avsforums.com - Both theater sites
of course,
www.arcadecontrols.comThere are other sites, such as the Bar Monkey, the build your own projector, numerous sites on how to build your own jukeboxes, but those escape me.
I'd really like to see a site that gets updated with new project ideas. Like a slashdot without the political ---That which is odiferous and causeth plants to grow---.