Dual boot XP/Vista sharing common installed applications and data?

I have a machine running XP with a full gamut of installed applications
(e.g. MS Office, iTunes, BDS2006, and many more).

This is a test and development machine, so I need to keep the XP environment
and all running application, but I want to also add Vista as a dual boot.

My question is whether it is possible for the Vista install to leave the XP
environment unchanged but copy the XP registry settings for the installed
applications into the Vista registry. Basically I would like the existing
applications to continue to work both under XP (existing) and Vista (new).

My reason is that for time and disk space reasons, I want to avoid having to
repeat the software installations of all these applications, and I want both
O/S to access the same "My Documents" folders. For example "My Music"
contains 50-60GB of stuff that I would like to access and add to from both
O/S instances.

{ Note: I did not yet decide whether to put Vista a) on a separate folder in
the same partition, b) on a different partition on the same drive, or c) on
a completely different drive; the most likely choice is c) but I think that
this is anyway irrelevant to my question... }