I have an iMac G5 with an Airport Extreme built-in. I recently got a G4
Tower ('Mystic' I think) and added a PCI wireless ethernet, a very
inexpensive card. Configuration turns out to be more convoluted than
expected; I guess it's a Realtek Mac driver, does anyone have experience
with it?

The symptom is, although the G5 claims to be broadcasting & file sharing
etc., and the G4's Realtek driver does indicate a connection to the G5,
the Finder on the G4 shows an icon for the G5 but no connection;
clicking on 'connect' yields a failure message, and none of the manual
attempts to enter IP, submask, & router have worked. Ideas?