It sounds like you know what you want already, and I agree. Your system will already run WoW just fine with what it has. But if you
must spend all the money I suppose I would look into the following:
-
Creative Sound Blaster X-Fi XtremeMusic Sound Card ~ $120
-
Sapphire Radeon X800GTO 256MB AGP 4X/8X ~ $170 (If it matters, it does have combo pricing with a plextor DVD burner)
You'll lose you tv tuner ability, but if you weren't using it in the first place I'd say the above videocard is a worthy upgrade.
And depending how much you have left I would either blow the rest on another 512MB stick of ram and/or a new keyboard/mouse setup.
Oh well, good luck!
Jam it back in, in the dark.