Alright.  You're worried about the registry.  So install the OS on external storage, too.

Can't do that on Windows?  (Whether you can will depend a lot on what kind of hardware you
are running on and what kind of external storage you are talking about.)  Maybe you might
want to consider an operating system that does not use a "registry"....


--
Cheers,
-- Mark Brinsmead
   Staff DBA,
   The Pythian Group
   http://www.pythian.com/blogs