If you are using the VPC we released in May, you can use this blog post to allow you to be able to use CRM as two web clients at the same time and show how different users have different views of the system. Well wouldn't you know, that isn't in the GUI of Windows Vista. Since I have been playing with demo'ing Vista and CRM, this sort of comes in handy. Chinmay Patel came to the rescue with a small piece of code that you can execute in a batch file to get the exact same results.
Take this small piece of code and place it in a text file on your desktop called Impersonate.bat (Or whatever you want...)
SET /P UN=Enter your User Name (domain\username):
runas /profile /user:%UN% "C:\Program Files\Internet Explorer\iexplore.exe http://urcrmserverurl:5555/"