Unlike the nForce 2, nVidia didn't put SoundStorm in 3 & 4. It wasn't getting the demand as hoped, so it was dropped. In general, I have seen many companies drop the gameport on all motherboard lines. With peripherials using USB for some time now, there's been no reason to keep it. It's no one's fault so much as that it's become a niche market. It is NOT a limitation of the nForce 3 chipset.
What you could do is try the card in different PCI slots and see if things work out better there. Is it showing up in Device Manager or not?