I made a new top for a bandsaw out of MDF board. The old top was metal and the ground wire was screwed down to it. Can I screw the ground wire to the MDF and ground it like it was with the old top?

MDF is medium density fiberboard, (think masonite or particle board) it's a wood product and non-conductive. You have to ground the metal structure of the bandsaw.

So to ground it I can just screw the ground wire directly to the metal frame and that will ground it?

Yes...

The ground wire ground where? House supply? Do you have 2 or 3 wire conductor?