Since there is no PPC that supports the HID profile today, you are stuck looking for a BT mouse which includes PPC specific drivers. AFAIK only one such device has even been announced. That is by Think Outside. Now whether the TO mouse driver would co-exist with the HP keyboard driver is a good question.
P.S. not a gamer myself, but agree that a BT gamepad would be a hot item. At least it would reduce all the 'buttons suck for gaming' posts
