Disclaimer

These instructions worked for me. They were culled from various web pages, forums or irc channels. I use a stock Zaurus SL-5500 with the Sharp ROMs and Qtopia environment. I have a 128 MB SD card (currently formatted as default FAT). I connect my Zaurus to the internet through the cradle with TCP/IP over USB to a Windows XP laptop.

1. Go to Administrative Options | Services
2. Start the Internet Connection sharing service
3. Open your connection settings
4. right click on your PC's LAN connection and select properties
5. Go to the advanced tab, enable Internet connection sharing.

On the Zaurus, edit /etc/resolv.conf to make sure your dns server is listed, if it's not, add a new line like this:
nameserver 12.15.22.52 (whatever your nameserver IP is)