[MP-Ryan]

-Buy an Antec Sonata Case.  I have the Sonata III and it is fantastic.  Also, the PSU it comes with is all that's necessary.
-If you're going with Vista, buy the Business edition.  It does not have all the bloat crap that Premium and Ultimate do, and you don't need Ultimate's encryption because TrueCrypt will do the job for you.
-Western Digital hard disks are crap and fail like crazy.  Buy a Seagate.  Better yet, buy two and mirror them through RAID.
-If you buy a sound card, I have an Auzentech and love it.  Much better than Creative with all the same (and more) features.

[General Battuta]

As for the case: that thing freaking loads in the bottom. I don't think I've ever seen a case like that before, and I don't think it's a good idea.

I may dual-boot Vista and XP.

I'm not too worried about the case; it's the best-reviewed model on NewEgg.

-Western Digital hard disks are crap and fail like crazy.  Buy a Seagate.  Better yet, buy two and mirror them through RAID.
-If you buy a sound card, I have an Auzentech and love it.  Much better than Creative with all the same (and more) features.

I like the hard drive idea.

What advantages would I get with a sound card?

[BloodEagle]

Just to clarify: I was talking about the PSU loading in the bottom of the case. Heat rises. Your video card will be right over the PSU.

What advantages would I get with a sound card?

Aside from not being tangled up by sound drivers for the mainboard, sound cards are far better at recording audio from a microphone. Not to mention a variety of special features which some sound cards support.