Windows Vista introduces a new 'Network Level Authentication' mechanism to RDP. It will be intereting to find out what they are doing there exactly, but meanwhile you might want to be able to use your legacy RDP clients to access your Vista desktop. Here is how you do this:

To configure Vista for the old RDP clients, go to Control Panel -> System -> Advanced System Settings. Select the "Remote" tab and then "Allow connections from computers running any version of Remote Desktop". That works - at the very least - good for mstsc.exe on Windows.

Here is a screen shot (Build 5342):

Now, the interesting thing would be to get this to work with rdesktop(1) and similar non-Windows RDP clients as well. Unfortunately, the latest Build 5342 is very uncooperative here. rdesktop fails miserably. Compare the TCP streams (upper one is rdesktop, lower one is mstsc.exe on Windows XP SP2):