I would personally always get a sound card. Even a cheap Sound Blaster would beat an internal one I believe, as it relives the CPU from any work.
As for the 8600GT, its not a great card no, but if you don't want to play Direct X 10 yet, and may update to a card later that supports Direct X 10, the Radeon X1950 Pro is still a very nice card, and beats the 8600GT by a bit, and costs only £100