It rocks but I ended up having to take VISTA off.
The reason, as usual apparently, is driver support. However, I had a hell of a time getting XP SP2 on my machine b/c it doesn't have drivers for the Tyan Tempest motherboard I have. Turned out that I had to turn off AHCI (whatever the SATA thing is) in order to get XP on my machine. Then I had to get drivers from Tyan's site. That in itself was an adventure. Their drivers are hidden on an FTP server and there is no mention of it on their web-site. Talk about fun. Luckily JNCS helped me out.
Overall this machine freaking flies. I'm also done installing everything on my machine. This go around the server stuff will live in a VPC. I ran VPC 2007 in VISTA and it worked great so I'll do the same in XP. Basically this means that my BizTalk and SQL work will be done on a different machine than my workstation.
I'm also going to attempt (again) to not run as a local admin on my machine. In some ways it would be easier to do if I was running 2003. Then I could just RDP back on to the machine when I needed admin rights. I'm talking to a friend about it and he bets it won't last long. going adminless is like going on the Atkins diet - sounds great for about a week. Then you give in to the dark side.