\"User A\" is logged on My application recognizes Environment.Username as \"User A\"
Now in Windows, I click on Switch user ... \"User B\" logs on
\"User A\'s\"
You definitely wont be finding the information at that level - you want to go to lower level APIs that enuemrate the logged on users (of which there can be more than one).
Something like How to write an application that supports the Fast User Switching feature by using Visual Basic .NET or Visual Basic 2005 in Windows XP ?
See also Architecture of Fast User Switching