Using Vista/Win7 common roaming profiles

Our school environment is currently on XP. We find with roaming profiles
and multiple users sharing the login (student class logins), you end up with
too many corrupt profiles left on machines all around causing all sorts of
problems. To get around this, I have a single user profile that accounts
only have read only access too when they log on. When they log off no
changes they make can be uploaded so no profile can be corrupted. Every
time the machine starts up or shuts down it runs a script while deletes
local copies of roaming profiles.

This has worked an absolute treat and fixed 99.9% of roaming profile issues
with our bulk use shared accounts. It also allows me a single account to
update wit changes for all students.

Under Vista/Win7 however it isn't working. Win7 only seems to work if there
is a %username%.V2 folder in the roaming profile path and therefore multiple
logins can't seem to just share a common read only profile. Even if I just
change the permissions on the profile folder the system creates to add
administrators to have access, the profile is no longer loaded and windows
claims the profile can't be found...

Are there any ways (AD/Group Policy etc) to get Vista/Win7 roaming profiles
to work like XP ones, being more flexible in their implementation... How do
you get multiple user accounts to share the same profile (they just map
different home drives for data).

Thanks in advance

Guy