Pazword seems to work ok :-
Also I think there is a commercial app that has been written for the cxx0 range. I have not tried it myself but the author hangs around in this board sometimes. Hopefully he will appear and give it a plug, and provide a link.
Here is the plug for SafeDee: www.bundu.com/zaurus.html
you can also search for SafeDee at www.handango.com
It has been optimised to work on the SL5x00 as well as in high res mode on the cxx0 range.
It isn't free, but you can download a trial version. This is fully functional except for import and export.
If it must be free, I have heard good reports about ZSafe, search for this on http://killefiz.de/zaurus/
Personally I prefer SafeDee, but then I am biased 8) .