XP/2000 server applying default mail prog

[markodude]

Hi ppl
I have a network with XP clients and 2000 servers. I need to make the default mail program for one group MS Outlook and for another Outlook Express. I can change the default program in the Internet and E-mail settings GPO but this changes it for all users and I want to restrict the changes on a per group basis.
Any ideas?
TIA