Hi,
The table at http://www.applefool.com/se30/#afpnetwork could perhaps be of interest to you. As you can see, the two operating systems are not compatible (at least not without modification, which is something that you normally do not want to do).
However, there are alternatives.
One could possibly be to install a small FTP server (like the now free NetPresenz) on the PowerBook G3, and then use an FTP client (or a web browser) at the modern Mac.
Another way could be to buy an inexpensive PC Card adapter for CompactFlash and a standard CompactFlash memory card. Used in a PC Card slot of the PowerBook G3, the CF card will act as a removable hard drive. Via a USB card reader, the files on the CF card could be read at a more modern computer.