Pentium 4 w/ Intel chipset. VIA chipsets are notorious because their problems with PCI bus control, USB and so forth. If the computer is targeted for music usage, I don't recommend any non-Intel-based system, unless you find vinyl-style crackling charming.
I honestly don't think there is need to wait about 8 months when 3.06 GHz HT-enabled Pentiums begin to be affordable. Virtually every Northwood P4 is a terrific overclocker, for instance almost every 1.8A chip overclocks to 2.7 GHz. Pretty powerful breed, the Northwoods, regarding both performance and overclockability.
Not to mention P4's come with a badass heatsink and a tiny <25 dBA fan. They won't get very hot. Should you choose to retain the original clock speed, your system will be very silent. You could actually concentrate on the music and not on the VIA crackling + Delta fan noise in an AMD system.
If you're going to build a server, consider a dual Intel Xeon system.
There's some more decisions to make with P4. Are you going for Rambus or DDR? RDRAM PC1066 is much, much faster than DDR400 but also much more expensive. Should you decide to use DDR, get a chipset with DDR333 support. Such include Intel's 845G and 845PE. Whatever memory should you choose, get 512 MB's of it.
Traditionally Asus has been the most respected motherboard manufacturer, but nowadays it has to compete with terrific brands like EPoX and Gigabyte. This applies for Intel and AMD systems.
A RAID setup might be worth considering for the HDD side. For instance, one 2x40GB striped RAID array for your multimedia and one regular IDE for your OS and crucial data. Striped RAID arrays are quite fast, althought a bit insecure.
And also, my 80GB 5.4 krpm Maxtor is extremely quiet. Western Digital 7.2 krpm 80GB HDD's (with 8MB cache) are the fastest in existence.
Display adapter. Duh. Radeon 9000 Pro or course. Good for anything, the image quality is good enough for CAD, it's powerful enough for games and it has plenty of outputs for your multimonitor or TV needs. Or a Radeon 9700 if you feel extremely rich.
Sound card. M-Audio Audiophile 2496, Echo Mia or Terratec EWX 24/96. This board is full of threads WHY these sound cards are better than 8-bit SoundBlaster 2.0.
Any DVD reader except Pioneer slot model. I own one (106S) and it's the noisiest, hottest and slowest DVD drive in history. Get any brand besides Pioneer. For CD-RW side, Plextor makes the best drives.
Okay, enough of the hardware blurb