To connect to a Windows box, simply open a terminal and enter
(Of course, you could enter the IP address of the machine you wish to connect to as well).
If you want to specify the user account with which to connect, enter:
rdesktop -u username myserver.com
where username is your preferred user account login name. If you would like to access the Remote Desktop session in full screen mode, enter:
rdesktop -u username -fP myserver.com
The -f switch indicates full screen while the -P sets up the bitmap cache for speed.