On Windows 2003, you can easily open Terminal Services Manager by clicking Start / Run / typing tsadmin [enter]

On Windows Server 2008 things are a little different.  I found this post on Scott Forsyth’s blog:

This doesn’t work in Windows Server 2008 anymore.  The change is ever so slight.  In Windows Server 2003 the tool was tsadmin.exe, so typing ‘tsadmin’ was all that was required to start the tool.  Now, in Windows Server 2008, this has been moved to a MMC snap-in and is called tsadmin.msc (plus tsadmin.dll is used silently).

So to fix this, click Start / Run / type tsadmin.msc [enter] and you’re good to go!