OK, so now I know I cant just format the drive I started again from scratch. I used BootCamp1.1Beta to remove the XPHome partition (needed a reboot grrr). Then I stated again from scratch.

When XPHome was installed and it went into a 'finding hardware' frenzy I sat back and let it settle down. Then I used the drivers disk, installed things and it all went fine(ish).

I still cant get my two video cards to work. There are a lot of devices in the DeviceManager that have exclamation marks next to them and I dont know how to fix this. XPHome only supports two processors as well. So Im not really getting the best out of my MacPro by running windows. Maybe Vista will be be flexible. Im not going to shell out for Windows Server!
I wonder what a 'Base System Device' is? Im assuming the PCI Express ports not working are stopping my second graphics card from being picked up. Im not really sure where to go from here but it is working well enough now for me to play BattleField 2 and PKR on it. A few people on the forums have made comments about drive speed but I didn't notice any problems.
Another disappointment for me is that I can't run Parallels using this hard drive. I need to create a new VM image with a new install of Windows. Im not sure I care enough to do that. This is a shame though.

Still At least I get a choice now. If you hold down the option key while the Mac is booting you see this

Pick an OS and off you go. Schweet.