Microsoft apparently has no easy way to set a remote windows machine to enable remote desktop access.
While you can use MMC to do a lot of management of a remote machine, allowing remote dekstop is (I guess) not one of them.
Intelliadmin has the cleverly named utility "Remote Desktop Enabler" to do this job.
And it is free. I have not tested it to enable on Vista but it works for enabling RDP on remote XP boxes. thanks Intelliadmin.