yeah if you're getting a pre built music pc, go for a carillon, we have one in the studio at work, and it's really well built, and already set up for audio work.

if you're building your own, go for a socket 939 64bit amd, you get more for your money plus they run cooler now than pentiums and perform better.

like dodgy said, get a sata 2 hard drive
motherboard manufacturers like asus and gigabyte are really good.
aluminium pc cases are really worth the money, i use coolermaster, but lian li are good too.

as for soundcards, like dodgy said, delta cards are decent, so too are emu and M audio, or you can pay much more and get a top end card.