if you can network Z to your computer over USB, you need to do the following
On Z:
1/ turn on IP forwarding "echo 1 > /proc/sys/net/ipv4/ip_forward"
2/ need iptables masquerading, e.g. "iptables -I POSTROUTING -o wlan0 -j MASQUERADE" on the Z - see lartc.org for lots of useful stuff about linux and NAT
On PC:
1/ set default route to the Z (or at least specific routes, e.g. to google "route add 209.85.229.0 netmask 255.255.255.0 zzz.zzz.zzz.zz" (from memory)
where zzz.zzz.zzz.zzz is the IP of the zaurus
this would also work if the Z had a bluetooth PAN connection or RFCOMM via a phone to the internet, although it would be quite slow!