On your desktop, type "ssh -l username -Y ipaddress" where username is the username on your zaurus (root by default, but it's a good idea to create a zaurus user and use that instead) and ipaddress is the ip address of your zaurus (type ifconfig to see the IP).
It should just work (as long as your password is not blank), or at least it does on my beta3 setup. If not, type /usr/sbin/sshd on your zaurus to start the ssh host service and then try again.
I had to enable X11 forwarding in /etc/ssh/sshd_config to get X11 forwarding to work (passing arguments to the ssh command doesn't seem to work).