from:http://www.krunk4ever.com/blog/2006/12/01/how-to-run-explorerexe-as-another-user/

So with the introduction of IE7, my little hack no longer worked, which was having the following shortcut: runas.exe /u:administrator "C:\Program Files\Internet Explorer\iexplore.exe"

With the IE7 update, when I enter C:\ into the location bar, it actually opens up a new Explorer window, running as my current user. Before it would automatically open C: drive in the same IE window and let me browse as administrator.

With this block, I decided to see if I could get explorer.exe to launch instead of going through iexplore.exe. Running explorer.exe from an administrator command prompt didn’t do anything. I was able to run start . and get an Explorer window opened, but that was running under me again. I search for explorer.exe switches and found this site: Command-Line Switches for Windows Explorer, however none of those switches seem to work. Calling explorer.exe /? returned immediately without displaying any kind of help.

Finally, I just went and searched for “how to launch explorer as another user” and found this: How do run Explorer as another user which had a very useful reply.

Apparently, the switch you have to pass in is /separate. At first I thought it was just a fake, but then realized I was spelling seperate incorrectly. If you execute the following command: runas.exe /u:administrator "explorer.exe /separate", you’ll be able to start explorer.exe as another user