Secure remote desktop login?

[Alan Dayley]

I'm specifying the configuration for secure, remote desktop login on a
Linux box.  Here are the basic requirements:

1 - User's computers are running Windows XP (or maybe 2000 but not
Vista) so the remote desktop client needs to run on Windows XP.
2 - The Linux desktop will be KDE (not that this should matter too much).
3 - At first the remote connection will be over the LAN, not over the
Internet (not that this should matter much either).
4 - The connection between the client and the desktop server must be encrypted.
5 - The user must not be allowed to copy files or other data from the
desktop server to their computer.  The user can only login and use the
server desktop.
6 - The user will login using credentials on the desktop server
independent of any other authentication mechanism.

I think FreeNX (http://freenx.berlios.de/) fits this bill.  But I
wanted to ask the group about any other options I may not know about.
I'm shooting for a FS/OSS solution but am not against paying for it if
that is the best thing to do.  (Meaning FS/OSS solutions that have pay
support are fine.)

Any thoughts?

Alan