Going by your username, I'm assuming it will be a VW related board? If so, realize that vwvortex is probably the biggest (certainly not the only) VW board.
I'm an admin on www.stratusphere.org, and a moderator on a few others, and am hosting one board for a friend of mine.
Even in on a msg. board with a LARGE following, I don't see the opportunity to make much money off of it. Most enthusiasts are there for the free information, and when talk of charging for anything comes up - only those that are down for the long run will donate anything.
As for advertising, you need to prove that YOUR message board stands above the rest, and will bring money into the company that is advertising. Chances are you'll get small vendors that won't want to pay for advertising, but will offer discounts to the group on purchases of their items - or group buys at most.

Not trying to shoot down what you want to do, but I've been there, and done that. :)