I'm too late!
PCs just plain suck for digital audio compared to a Mac, mainly because you're stuck with Windows OS (and run the risk of wearing out the reset button). Mac OS X (I have 10.3) is hands-down the most stable OS on any computer ever. I believe that new Macs now ship with GarageBand (or you can get it for ~$50, even cheaper on edu discount), which is dead simple to use with a USB or Firewire digital audio interface. GarageBand was a direct result of Apple's purchase of Emagic last year.
If you're ever wanting to record multiple tracks simultaneously (i.e. in a live situation), on Macs the Firewire path is direct to the CPU. On PCs the Firewire path shares the same databus as all the USB stuff, resulting in a throughput bottleneck that Macs just don't have.
Finally...Emagic's Logic 6 Pro is now available through the Apple Store web site. It sells for $999 but the edu discount brings it down to $299
For which you get:
A**-kicking audio & MIDI recording (unlimited # of tracks)
24 bit/96k capability
a bunch of really good effects (EQs, compressors, delays, sub-bass, you name it)
a bunch of really good software synths (they used to come $eparately)
mastering and burn-to-CD or MP3 capability
more features than the mere mortal can comprehend in a lifetime
For mastering I don't even use regular monitors. I take my Mac (mine's a laptop), route the output of my audio interface right into my car stereo, and just master in my car. If it then sounds good on the home stereo too (which is does ~80% of the time, the low end is the trickiest), you're done. Burn it!
More expensive, but well worth it.