Yeah, see. It sounds to me like the only things you could possibly keep in an upgrade are the sound card and the tower. The RAM is likely DDR, which isn't used in new mobos, the 9800XT is AGP which isn't used, the motherboard would only support old processors and you're looking to game so you need power.
New mobo, processor, RAM, video card, and PSU sound like a need if you're going to play new games.