The only things I have to add are:
I think the price point has moved on on cpu chips. Unless you're trying to shave all your costs (and at $2K for the computer you clearly don't have to do that), I'd go for at least a 2.4 gHz P4, that's where the sweet spot on price has been for a while.
Asus boards tend to have a great rep and they'd be at or near the top of my list. I've also had excellent experience with my iWill board.
HD space: the more the better, but by many accounts you'll get a performance edge by using one HD for apps and OS and one for data. Partitioning appears to be a marginal issue. I've seen people recommend against partitioning with the audio data on the partition and I've seen people recommend it. I lean away from it but I suspect there's no hit from the partition itself, if you wanted to keep a mirror copy of your OS on it or some such while you have your OS, apps, and audio data on the main partition. (As I understand it, too, it's supposedly the read head "skipping" around the HD to service the OS and the audio data. I've also read/heard very convincing descriptions of why this happens anyway whether or not there's an intervening partition. So... who knows.)
But a separate partition is not nearly as safe as a separate HD.
And if you use a separate HD, you'll probably want to make sure it's on its own IDE channel. The recommendation I've seen is: OS/apps HD on first channel by itself. Audio data HD on the second channel as master and CDR as slave. Or even use an open PCI slot to put in the fasted IDE controller available feeding drive(s) to match. (So that the HDs don't have to share a channel with a CD...)
And, of course, even if you don't go with a separate controller (overkill, I think for most of us) you absolutely want to get a MB with the latest IDE controller standard on it (Fast-ATA-133 still it?) and HD's to match (although if you can only afford one very fast HD it's best to make it the audio data drive -- since most apps/OS don't require anywhere near the amount of data transfer that your audio data will if you're doing heavy lifting.
With regards to drives: I myself stay away from exotic high RPM drives (10,000 and 12,000 RPM drives). It's true that you'll get the ultimate performance from one of these hooked up to a fast SCSI controller -- but many of the HD horror stories I've heard in recent years involved high speed drives.
That said, I haven't heard hardly any HD hardware failures involving consumer drives in recent years. And in 18 years of desktop computing, I've only had one HD fail (although I have had bad software corrupt drives on occasion. The old AOL installer and update software was notorious for corrupting HDs. Also Apple's QuickTime has been known to corrupt Windows HD's on installation. It's rare but it has happened -- to me (and I also had QT corrupt my BIOS, something I didn't think was possible but, since there was no other reasonable explanation (the QT install killed the machine right there and ONLY re-flashing the BIOS got it running again after an ENORMOUS diagnostic effort that involved swapping everything but the MB, CPU, and RAM... which was how I came to the conclusion I should re-flash the BIOS).
Anyhow, that one HD I did have a hardware failure with was mounted transversely (sideways) rather than horizontal to the ground. My former hardware guru told me that wasn't a problem with modern HDs but I think I outgrew him and the level of advice he offered (my new slogan: No master, no teacher, no guru: no BS.)
Recently I've used Maxtor (about 3 years ago), IBM (about 2 years ago) and Western Digital. And even though that one dead HD was a WD, I still recommend WD. They run noticeably quieter than the IBM (a 60 GB) and Maxtor (a 20 GB -- both were 7200 RPM ATA). I'm now running an 80 GB and a 160 GB WD.
One caveat: STAY AWAY from that stupid software that WD and others put in their HD packages to "help" you with older OS's or BIOS's that don't natively support large partitions. If you've got a HD that's bigger than your OS or Bios can address directly -- partition it!!!
Don't mess with the remapping software! (In fact, when I installed the 160 GB recently, I was foggy headed -- no coffee yet -- and got confused about how big a drive I could support (running XP Home -- btw, if you do any computer developing or use your computer to VPN or network with XP Pro networks DO NOT get XP Home. I wish to heck I hadn't decided to save the dough... but that might not effect you and XP Home is otherwise fine) -- anyhow, foggy headed, I thought for a few moments that I would have to run the WD software -- but it crashed when I tried to install it. THinking the disk that came with the HD must be buggy I DL'd the latest version from the WD site and IT crashed too! Anyhow, I reread my material and realized I shouldn't have any problems addressing the full 160 (or actually the 152 or so MB that it actually works out to). I just installed the drive and formatted it and everything is fine.
Finally... I know it can go both ways, but I'd be a bit leery of a MB with a built-in soundcard. Windows usually supports multiple sound cards with no problems whatsoever (I've run multiple audio devices since '96 but before Plug-n-Play was perfected it could be a ***** getting things in agreement. But after Win98 things were pretty slick.) If you want a SoundBlaster for gaming and/or for the Emu-designed SoundFont synthesizer built into them, I think I'd go with one on a discrete PCI card. I've heard stories of SB chipsets on MBs not supporting the full range of SB functionality. In fact, I know at least one person who disabled the SB built onto their MB and bought a $30 SB Live PCI card (they also had a pro-sumer card they used for audio recording but they were big into Sound FOnts).
I'd build it all around that tbh.