the particular hardware I'm thinking of installing. Unless you're lucky and run into a real expert, any given message board you may be unlikely to have a member who's tried exactly what you're contemplating
Is there a real reason for insisting on wireless for the tower? A direct ethernet cable connection might actually be faster, easier to set up, and more reliable. If your friend has wireless internet for a different computer (say a laptop or netbook), you might be able to run wire from the base station to the G4, depending
About a year ago TUAW was recommending nQuicky for use with the appropriate Apple base station if there was an available PCI slot in the G4. It's usually not hard to pop something into a PCI slot, taking appropriate static precautions, but I'd try to down load the manual and read it before deciding on that
http://www.tuaw.com/2009/05/14/ask-tuaw-wifi-on-an-older-powermac-creating-contact-sheets-ma/ http://www.quickertek.com/products/nquicky_pci.php