Help Please - Remote Desktop Sharing in a Vista & Win2K estate

I hope some one can help..

The company I am working with is undergoing a massive client refresh of all
its desktops, laptops and tablets moving from Win2k/XP Pro to Vista Ultimate.
Currently the helpdesks use either SMS2003 or NetMeeting to access a clients
machine to help resolve issues at first line. Now as you are probably aware
Vista can not be controlled by SMS2003, even SP3, and NetMeeting can not be
used by the service desk to share the desktop.

I looked to Win Meeting Space for support but it requires a number of
services including IPv6 which is not deployed on the companies network
infrastrcuture. So that leaves RDP! Alas RDP logs the user off as the remote
user logs on so it is greatly limited for working through a problem.

Can anyone help? Am I missing something obvious aside from a 3rd party
toolset?