Often I have had problems logging in to remote desktops because the two user sessions Microsoft allows you to have are occupied. This is very annoying and until Windows Server 2008, you got no choice to log of the other users. There is however a smart little command line tool to do this.

To see logged in users, type: qwinsta /server:SERVERNAME
To log out an existing session, type: rwinsta /server:SERVERNAME SESSIONNAME

Here is an example from my machine:

C:\Users\gm>qwinsta /server:kraftwerk
 SESSIONNAME       USERNAME                 ID  STATE   TYPE        DEVICE
 services                                    0  Disc
 console                                     1  Conn
 rdp-tcp#0         gm                        2  Active  rdpwd
 rdp-tcp                                 65536  Listen

C:\Users\gm>rwinsta /server:kraftwerk rdp-tcp#0