Actually writing a messageboard script (suite) is pretty trivial at least if you interface with a database (flatfiles are ok but you have to be tricky if you want it to scale well with a large messagebase) - it's just a whole lot of work.

If anyone wants to have a look, I suggest ikonBoard v3 - free and seems to be decent Perl. (And just like IlyaM, I don't work for them.)