I remember there is a way to have a XP mode program run seemlessly in windows 7, and it has a red border around it. That way it just uses your current credentials and the users don't even really have to do anything different.
For the life of me I can't remember what it is called, let me Google a bit.
edit: I think it might just be Seamless mode, but the name doesn't seem right at all.
http://www.hanselman.com/blog/Window...atibility.aspx might give you some idea. I am going to look through my documentation and see if I can find it.
edit2: It's called Microsoft Enterprise Desktop Virtualization (MED-V) - Short video
here