Sound blaster Audigy and ATI Radeon 9700 should be in your list of things to get if you want the best graphics and best sound. Aren't Soundblaster Audigy 2's out?
As for speakers, nothing beats Klipsch Promedia 5.1's, but they are like $400 shipped. Logitech's THX-certified, 400 watt Dolby Digital setup (the Z-560), which is $150 shipped from www.newegg.com
(what I have), and perfectly fine for shaking floors, blowing ear drums, and excellent sound quality.