I've worked with Vista on a Mac Pro using boot camp and have not found it to be the easiest installation. Windows Vista has trouble being made the secondary partition on a secondary drive and will not allow you to install it from booting the DVD under certain conditions. A general workaround I found to any issues with Vista not being satisfied with the drive configuration is rather simple and also works if XP is already on the machine and it won't upgrade:
- Install Windows XP (if not already on)
- Start Windows XP
- Open Vista installer from XP and do a custom install
- Have the installer leave the partitions intact, but move the XP stuff to a folder (Windows.old)
This setup will keep your partition setup exactly the way Boot Camp likes it for XP (no removal of the EFI partition, for example) and opens up some less conventional options like installing on the second, third, or fourth drive on the Mac Pro even if Vista won't let you. Beyond that, the Mac Pro seems to run very well with Vista. Sound and graphics drivers work fine, although the sound drivers seem to take a little work to get just right. Also, it does not seem currently possible to use the Boot Camp installation of Vista with the new RC for Parallels like you can with XP (i.e. dual boot and virtualize from one install of the OS on a physical partition). It may be possible soon, as Parallels seems to get updated quickly or there may be some particular tinkering that makes it work.
Personally, after working with Vista for a little while, I think I prefer Windows XP since I only use Windows for a few games and programs from time to time and don't need an OS that uses 512MB of RAM when it idles to do that. The performance hit of going from XP to Vista is similar to going from Mac OS 9.1 to Mac OS 10.0 and Vista can be almost as buggy in parts. The best bet is to wait for a little more optimization and patches. Besides, by then Boot Camp and Parallels will have much better native support for Vista.