digisage, if your server is running windows server 2003 then it probably has rdp 6 (which vista also has).

On Vista, i need to go into remote desktop and 'Allow connections from computers running any version of Remote Desktop (less secure)' instead of default higher security option using network level authentication. This added security was put in for RDP 6.0 (winserver2003/vista) and the open source rdesktop client does not support that (yet?) Since microsoft built the mac version i guess that version is kept up to date with security of rdp 6.

Also the command line build i did supports -0 option to connect to server console (if thats what your trying to do)