Is there a way to use rdesktop or another Linux client to connect to a server that requires Network Level Authentication?
From Windows Server 2008 R2 — Control Panel — System And Security — System — Allow Remote Access there is an option that says "Allow connections only from computers running Remote Desktop with Network Level Authentication". So with this enabled I can con not connect from Linux. I can connect from XP but you need SP3 and I had to edit a couple of things in the registry for it to work.
Best Answer
FreeRDP (a spin-off from rdesktop) supports this in recent versions.