Morning,
During the summer we moved our School (George Spencer) to Windows 7. Except for odd bits of hardware that are still running windows xp.
So Currently: 600 machines windows 7 and 100 xp machines.
Fully windows 7 windows xp mixed environment and working perfectly.
Both mandatory and roaming user profiles using the .V2 extension.
We also have implemented WMI Filters as the major problem we faced were printer drivers between the two operating systems.
In regards to the admx, you are not required to run windows 7 machines on admx. However if you wish to actually restrict the user you would either have to turn one of your DCís to 2008 (recommend 2008 R2) server (this would copy the admx files for you or manualy copy the admx files yourself).
We also noticed odd behaviour with redirected desktop backgrounds and start menus and had to add manual registry files.
On a side note for anyone having problems we at George Spencer School run an ICT Company called Advanced IT Services based in Nottingham and currently offering free ICT audits for other schools and colleges. Contact me via pdixon@advanceditservices.co.uk