I think there's an artical on the
www.shirtpocket.co.uk forum on GPS use with a Z with a GPS card, however, it may be worth setting some sort of expectation here.
If you want to use GPS well with a card then you really need Route Planning software and I'm not aware of any real Route Planning software for the Z.
The problem is actually judging the best route from A to B. Most commercial systems use GPS to pinpoint your location then use onboard route planning to plan your route.
There is a thing called Waypoints with GPS that gives rough routes between co-ordinates but I'm afraid that I'm not that well up on GPS to say how functional that is.
Most of the suggested GPS software available for the Zaurus is aimed at tracking your location against a map to show you where you are and with many it's up to you to provide a big JPEG of a map and calibrate the software to that map.
Personally I don't think it's the greatest tool for GPS unless you want Maritime Navigation where I believe there are some more useful packages.
I would suggest a TomTom Go as product to do car based nav on a budget (£500 or less - compared with £1000+ Garmin/Megellan systems).
Sorry if this is not what you want to hear and I would be interested if anyone else has any more positive news on features available for the Z.