Go with a fast P4 and exessive amounts of RAM and you're set for music apps. A nice HD is good too, like the Barracuda V Special Edition from Seagate. Graphics don't really matter that much, unless you play games. Parhelia sucks compared to Geforce or Radeon. The supreme 2d quality is just hype and marketing. You need parhelia if you plan on usin 3 monitors, but not otherwise.
I'm using two monitors. One with a GF3Ti500 and one with an old GF2mx400. It's great to be able to move things into the 2nd screen. It works as extra desktop space. You'll need XP pro for this. Some GF cards can have two screens attached to them, but they'll share the same graphics memory and CPU.
-tek