This might be a more general WiFi issue rather than something specific to the Zaurus, but this is the first time I've run into it.
I connect the Zaurus to my WiFi network and I use the network on it just fine. If I switch to my desktop and ping the Zaurus it succeeds just fine. I then leave the Zaurus alone for a while, still switched on etc but not using the network. After maybe something like 5 mins or so I try to ping the Zaurus again but this time it fails saying that there is no route to host. The Zaurus still says it is connected to the network and the webpage of my access point still lists the Zaurus as being associated with it. I then use the network from the Zaurus, eg. browse a webpage, and after that the Zaurus is pingable again.
Any ideas what causes this behaviour?