For anyone that has had to boot Windows into debug mode to do some digging around (like remote Kernel Debugging), things have changed. In the past, you could open up boot.ini in the root of the system volume, and add a "/debug" flag to the Windows OS record of choice.
One of the things you might notice with Vista is that boot.ini is now gone, solid gone. So, with boot.ini gone, how do you boot into debug mode? It is done with a new tool called "bcdedit". In the root of the system volume, you'll notice a hidden system directory "Boot" which is the Boot Configuration Data store. So, to turn on Kernel Debugging with Vista, you can now execute "bcdedit /debug on" (be aware, you need to be running the command prompt under an account with Admin privileges).
If you want to see the load of stuff you can do with bcdedit now, just execute "bcdedit /?".