Despite the fact that we've been happily using Windows 7 on a Boot Camp partition on the Mac Pro in our office since the launch of the OS some months ago, Apple has now given its official blessing to Microsoft's latest offering, which we like to call Windows 7ista.
The official Apple line for some unfathomable reason is that you must have a copy of Vista installed in order to install Windows 7, and the Boot Camp updaters supplied will only run in that OS.
The upgrade fixes a number of bugs, none of which we were aware of, but they include trackpad problems and compatibility problems with Apple's Magic Mouse and wireless keyboard.
If you really feel the need to sully your Mac with Microsoft's OS you'll need an Intel Mac and Snow Leopard 10.6, at least, to get the best out of it.
Thirty-two and 64-bit versions of the updater and all the information you'll need to get started are available here.