I use...
I have a Mac Pro 1,1 with 4 1TB, in this config:
Bay 1, installed XP x64, there are some old forum post for pseudo-bootcamp hacks
Take out Bay 1 drive
Bay 2, installed Win7 x64, using "some kind of efi conditioning" here are the links I saved
http://timothybrown.tumblr.com/post/110271493/installing-windows-7-x64-on-a-mac-pro-late-2006
Bay 3 and Bay 4 RAID 1 Mirror with Lion Installed
External FW 800 1 TB for Backup
Everything has been running for 2 years no problems.
I use WinClone 3.5 to make image backups of the Windows volumes
If you ever need to start over you make a "Just installed version" image (WinClone) about 16-32 GB depending what you want as your base, and you never have to take out XP bay 1/2 drive if you need to redo your install of Windows 7 or XP x64. Select Vista MBR option in WinClone and the XP ini option. Use option key to boot pick your Windows version. You have to format GUID for Windows 7, for everything to be smooth, and MBR for XP x64. If you setup the XP x64 hacks you can use the Bootcamp Control Panel in XP x64 and Win 7 x64 to pick your Boot Volume, oh you also need Paragon NTFS, to make the boot volume a windows one in Lion.
It has a Radeon 5770 and 16 GB so for Mountain Lion there are some work arounds but it would be miserable, which is fine why? I am getting a 2013 Mac Pro and this machine will be my PC for gaming with a KVM.
Oh you need this for Bootcamp 4 drivers
http://www.wintellect.com/CS/blogs/...s-x-10-6-snow-leopard-windows-7-x64-love.aspx
Download them from some other Machine, I don't think you can get them while running Lion on 1,1. I can't remember. I downed them from my MacBook Pro and did the msiexec line in cmd, that will run the msi and install the drivers, the location is tricky I think but you can figure the rest out
Have fun