I have been a PC user since 1991, and I have used Macs only intermittently as circumstances allowed. Now I use both and I love both, although if this comparison were based on the sheer beauty of the gui...Mac wins hands-down.
I have a 12" ibook g4 that I bought in January, I upgraded the RAM to 1.2 gig, and I bought and external firewire hard drive and along with
my m-audio omnistudio usb I have been recording like a madman, using GarageBand, Tracktion, and Logic Express. I got the iBook initially because I needed a laptop and I fell totally in love with OS X when my friend Anne bought her powerbook a few years ago. So I went with a Mac, thinking I might do some recording with it, but mostly to do my day to day tasks. Then I decided to hook up my Omnistudio and played with garageband and I was quickly addicted. The thing that really pulled me in was the completely painless process of hooking up the hardware and getting going. It took less than five minutes and I was tracking, and then when I tried the other software, setup was also a breeze.
My PC, however, was where I started recording, and I learned most of what I know from recording from it. And, since I switched to XP, I have had zero stability issues, even with the PC being used for internet and games. I have an AMD Athlon 64 3000 with 512mg RAM and a 120gb hd. It is a great machine and I honestly have to say that the only reason I see to use my mac over my PC is that the mac is easier on the eyes.
Now with all this in mind, I would have to say that if you want something that will work great out of the box and looks beautiful, go with a mac. If you don't mind Windows's clunky appearance and don't mind doing some configuration work (i.e. removing unused services from startup, manually configuring page file, etc.) the a PC running windows XP will work fine for you. As far as software goes, for Windows I would recommend SONAR 2.0 or later, a very powerful program and inexpensive if you buy the earlier version.
Just based on what you have said it seems like you are ready to make a switch. Go with the Mac. You will love it and when your project is done you will miss it terribly and end up buying your very own.