You can get a cheaper LG drive that has Lightscribe, it's a 22X dvd burner. Also, you should get an X48 mobo so you have room to upgrade. It has a noticeable performance increase compared to P45 when in Crossfire. I like the Cooler Master RC-690 but I'm guessing you like the Antec. Same with the hard drives, I prefer WD Caviars, but I guess Seagate is your preference. Nice build.
Will the Creative Labs - Sound Blaster Audigy SE 7.1 work well with Vista? They just released new drivers for the Audigy 2 Value card I have, and the latest X-FI drivers are still in beta. You might be better off just using the mobo's built in sound than getting the Audigy SE.
P45 can use Nvidia. He meant only ATI in multi-GPU systems. They support Crossfire but not SLI. the 4870X2 does not require crossfire. I think it'll be an amazing card. If you won't be using more than one card, stay with a P45.