Well, this has nothing to do with the Zaurus or the Mac. ssh is a standard unix program. But it won't help you enter data on applications, only command line stuff (for the experts: ssh -X, yes I know). You can use something called VNC to do what you want but I never did this on a Zaurus or a Mac, but maybe there is info on the forum.
Anyway, to use ssh. I assume your Zaurus and your Mac are connected. Open a terminal on the Zaurus, become root and type "sshd" and return. Now on the Mac, open a terminal, type "ssh zaurus@<ip-of-the-zaurus>" and return. Then you type your password and off you go. Replace <ip-of-the-zaurus> by the ip address the Zaurus has.
There is tons of information about ssh on the web but it may not be what you want.
Um abraco
Felipe
p.s. Maybe ssh is not installed by default on the Zaurus but you can find the ipk on ELSI. It certainly is installed on the Mac.