making remote desktop active before log in

[Eric S. Johansson]

the remote desktop feature is wonderful.  But there's one problem which 
is that it is not available until someone has logged into the desktop. 
Is there any way to use VNC to login to the ubuntu authentication screen 
remotely and then enter a username and password to bring up a desktop?

if there isn't, is there anyway to activate a desktop from an ssh 
session which would make the remote desktop feature available at that point?

thanks
--- eric