I installed Windows Vista on our Mac mini. I wanted to document the process, in case I need to do this again.
When I started, I use the Mac OS X installer to create two partitions. One 12Gb partion for Mac OS X and the rest for windows. This didn't work, as BootCamp can not be enabled unless you have more than several GB of space availble. So, I had to create one partition and then reinstall Mac OS X. Once I did that, then I could use the Boot Camp installer to resize the Mac OS X partition and install Windows.
The other problem that I had was that the DVD drive on the Mac mini is starting to malfunction. I was able to install Mac OS X by putting the Mac mini in Firewire Disk Mode, and using the MacBook Pro to actually do the installation. Unfortunately, you can not install Windows like this. You only can enable Boot Camp on the internal drive. Also, you can't use an external USB DVD drive to install windows, as Mac hardware. Luckily, I was able to get Vista installed by rebooting without the DVD inserted, and the option key held down. Then when in the disk selection screen appears, insert the Windows DVD, and then boot into the installer.
I was using our LCD TV as a monitor for the Mac Mini. Once Windows was installed, I wasn't able to see any video when setup assistant started. I had to switch to a different monitor that supported that resolution so I could finish the setup.
Once, I installed Apple's drivers everything worked perfectly. Media Center works on this, and I am able to access this on the Xbox through Media Center extender.