Easiest way is to setup one Powerbook as an Airport host:
- Click on the Airport icon on the menu bar
- Click "Create Network ..."
- Setup a network name, etc, and click OK.
Then, from the other computer, click the Airport icon in the menu bar and connect to the first Powerbook.
Once that is done, go into system preferences on each machine, then Sharing, and turn on Apple File Sharing on each machine.
You can then, from the Finder, choose Go --> Connect to Network. Select the other computer, and you can then drag and drop files onto it. Hope that makes sense.