A better idea for PowerMacs
Buy a PCI Airport Extreme card which has the Broadcom (needs to be correct) chipset.
Sonnet sells one currently that works flawlessly, and it supports 802.11G and B.
Linksys produced one for a while, as well as Buffalo, Microsoft and several other vendors.
Silly to pay $100 for 802.11b..
The Sonnet is a sure fire fix. The other brands you need to research to find the right version of the card. I currently have a Sonnet, a Buffalo PCMCIA card and a Linksys PCMCIA, all look just like an Airport Extreme card (in a MDD, a Pismo and a once was Wallstreet).