i was looking for the thread where it's already discussed but i'm having internet problems so i'll just hash it out from memory.
- go into gp2x settins menu, set "menu extension" to on.
- set the ip address to something reserved for lans like 192.168.x.x or 10.x.x.x
- scroll down, set "usb network" and "samba server" to on.
- windows will find the hardware and ask for a driver. get it from the file archive.
- go into network connections in windows, click properties for the new one (should say linux on it) and set the IP address and subnet mask.
now it might take a while but eventually you should be able to go into windows explorer and type "\\gp2x" and get a response.