Launch IE as a different user

Thunderstone Search Appliance Manual

Launch IE as a different user

When testing multiple user accounts, you can Right-Click on an Internet Explorer shortcut, select Run As..., and enter another user's credentials to launch Internet Explorer as that user. This way you can try out IE as them without needing to go through the full login process.

Note that the user you run IE as must have logged in at least once in order to properly configure IE, otherwise the Add to Local Internet dialog will not function properly.
If there is no Run As... option, create a new shortcut to Internet Explorer and use that - the IE icon on that's on the desktop by default is not a normal shortcut.
You cannot test another user by entering their credentials within the browser when accessing the proxy machine. Credentials MUST be passed to the proxy machine automatically by IE by having the proxy machine in IE's Local Internet settings.
If credentials are entered manually in IE when accessing the proxy machine (even the credentials of the current user), then IE will use NTLM to authenticate with the proxy machine instead of Active Directory, which prevents proper delegation from occurring.