Current desktop as in the System Console?
Kinda. If you mean take over the existing logged in session on the server
(like with VNC or PCAnywhere) you can do it to a point. Meaning if someone
else is conencted to it and you try to connect it basically logs them off
and logs you into the console.
The way to access it is via a /console switch added to the client executable
so :MSTSC.EXE /CONSOLE
(Only works with 2003)