You can serve a webpage from a GP32 using GP32 Linux and a hand-compiled version of Apache. With enough work you could probably get mod_php and MySQL running on it, and get some kind of BBS up and running whether or not it's IPB.
However, I'm not sure I'd trust a GP32 to run things as meaty as Apache and mod_php with the amount of RAM it has free; I'd use something like tinyhttpd and maybe (maybe) some kind of php handler for it. SQL might be insane, so you'd want to use a flatfile bbs provider like YaBB.