That motherboard is seen here:
http://motherboards.org/mobot/mother...hips/M756LMRT/
It does appear to have an AGP 4X slot that you could put a card into although I see another version under the same ID that does not have an AGP slot.
As I mentioned I do not know the Audition game but Maple Story will not play on this computer unless you add an AGP card. Then again it is questionable. You would probably need to update the BIOS as well at least. You would need a 3D card that supported DirectX 9.0c.
In my opinion it is not worth upgrading this computer. You'd be better off looking for something new for gaming.