I tried installing the Windows 7 beta. It was the first time I'd ever tried using Boot Camp. Kind of a pain in the butt, because Boot Camp couldn't install a Windows partition... I had to do a Time Machine backup of OS X, reinstall OS X, then make a partition for Windows, installed Windows 7, then restored from Time Machine.
Several hours of waiting. Afterwards, I couldn't get the video driver to work (2600XT), and it got so annoying I dumped Windows 7. But I realized I would like to have Windows on here, just in case.
So I went to Microcenter, bought another hard drive and an OEM copy of 64-bit Vista. I moved my OS X installation from the original hard drive (the 300GB one) to the new one (1TB)... had planned to install Vista on the old one, which I put in bay 4... but during the Vista installation, it said the computer couldn't boot from that drive. I wonder if there's some limitation that the computer can't boot from a drive in bay 4.
In the end, I just split the new hard drive 50/50... OS X on one half, Vista on the other. At least the installation went smoothly.
Now if only I could get my Duet to work in Vista (not holding breath). Heheheh.
There is no limitation with booting from a HDD installed in Bay4. My SSD with windows 7 is installed in Bay 4 and boots fine.