I use a small (cig. packet sized) wifi/ethernet adapter. It can work either as a little access point (plug it in the ethernet port and connect via wi-fi), or as a wi-fi adapter (plug it in the ethernet port on a computer and you now have a wi-fi interface). It can be powered either by a separate power unit, or from an USB port (usb-to-power cable).
A BT access point sounds like a good idea too, I was however just thinking about the N800 setup.. out of the box the wizard seems to want to connect to BT devices with a Phone profile only, so presumably you'll have to do the setup manually. But this could be the best solution for workplaces where you're not allowed to put a wi-fi AP onto their internal network (understandable!). BT devices are paired, after all, and class 2 devices have short range.

EDIT: Aha.. no N800.. so the wizard remark doesn't apply. Anyway my own Zaurus (old SL series) doesn't have BT at all.