remote desktop (terminal server client doesn't work accessing a linux/virtualbox machine)

Trying to use my Jornada 720 (with terminal server client Build 0179) to access desktop on another machine running remote desktop (RDP) protocol on port 3389. The server is virtualbox running on a linux host, and "access method" is set to "null".

The Jornada 720 times out when I enter the IP address of the server.

I have verified connectivity on LAN between the Jornada and the same linux machine using ssh.

I'm new to remote desktop (I've always used VNC in the past, but virtualbox remote access is via RDP, not VNC.)

Are there any alternative remote desktop clients I should try?

Thanks,

Dave