- Download Windows ISO from Microsoft website.
- Follow steps from
this website (you'll have to do it on Windows, on some other PC) prior to burning ISO to DVD
- Make sure you Windows HD is in the first slot of your Mac Pro
- Install Windows through Bootcamp or just boot into DVD by holding Option (Alt)
- After booting into it, install Bootcamp Drivers through Command Prompt, running BootCamp64.msi
That should be it IIRC.