This is a very niche trick because Vista and Server 2008 apparently no longer support the runas command. However, my company is still using Windows XP and I imagine that there are plenty of others out there as well...

Anyway, I have been developing a web app which uses a SSO (single sign on) mechanism. In my code I grab the users ID and domain name then do some lookups in Active Directory. Then I take the results and store this information (in session variables) for later use. In my markup I have some if statements wrapped around certain sections of the page that are intended for application administrators only.

In order to test the application with different LAN IDs I launch IE using the runas command. This is something that I have been doing since IE6 and it worked all the way until I upgraded to IE8. Since, I hate logging in and out in order to test my web application I really needed to make IE8 play nicely with runas.

After a bit of searching it seems that IE8 has blocked runas because they wanted to close a security loophole. Apparently, IE8 prevents someone from having two browser sessions open that are running under different user credentials. Well fortunately, through the magic of registry hacking we can disable this:

1)  Open RegEdit (Start > Run > regedit )
2)  Browse to HKEY_LOCALMACHINE -> SOFTWARE -> Microsoft -> Internet Explorer -> Main
3)  Add a dword under this key called TabProcGrowth
4)  Set TabProcGrowth to 0

Note: I am not responsible if you blow up your machine from hacking the registry. Always backup your registry keys before making any changes.