Vista - Replacing the Reg keys and boot sector files

I know this is a total long shot that is most likely not going to work, but I
just got courious....Say I replaced all the Registry entries and boots sector
info on my Vista computer with thoughs of a Win 2000 or even XP, what would
happen? An error more than likely, or would it reboot in to 2000/XP?

All that I can envisage happening is your blood pressure spiking, and once that has settled, a reformat and reload of Vista.

First off, replacing the boot sector does nothing to change to operating system, as all the files and programs that make Vista are still in place. If by some statistically impossible miracle, Vista does boot, then the replacement of the registry files will give it a hernia that will more than likely give it a bad case of BSOD, should you be that lucky.

Someone on this NG once gave a perfect explanation that I think applies here too. Doing this and hoping Vista will still boot is like choosing the least destructive nuclear bomb. It's a bad idea to begin with!