Using Windows Server 2003??  Have you installed VMWare Server??  Chances are you're stuck in this boat.  Fortunately for you, I've done the hours of legwork necesary to find out why it is that your ASP.net tab disappeared from IIS.

For whatever reason, even though you probably are not using the 64 bit version of Windows 2003 R2, VMWare Server adds a line to metabase.xml found in c:\windows\system32\inetsrv.  The line you are looking for says "Enable32BItAppOnWin64=TRUE" or something of that sort.  The fix is simple:

1. Shut down the IIS Admin Service
2. locate the metabase.xml file in c:\windows\system32\inetsrv and open it in notepad or your favorite xml editor
3. Search for, and delete the line containing the text "Enable32BitAppOnWin64"
4. Save the file
5. Restart the IIS Admin Service (and any other services that had to be stopped in order to stop IIS Admin)
6. Check IIS

The ASP.net tab should now be back and you should be able to set the ASP .net version as you always have.

Now, if you are fortunate enough to be reading my blog before you decide to install VMWare Server, you have three options

1. Install VMWare without the Administration Website
2. Open IIS and backup your IIS configuration using the right click menus.  Install VMWare, and then restore your configuration.
3. Don't install VMWare Server (nah….)

Hope this helps!