So I added airport n to my G5. Check this out. I bought this mini pcie to pcie adapter card and put an apple airport card in it and it totally detected it and works perfect. Nice upgrade for anyone looking to add some faster wifi to their G5. Here is the link to the ebay auction for the adapter. Any pcie airport card will work. I used one from an old imac.
Mini PCI-E to PCI-E Wireless Adapter 3 Antenna WiFi Walan For Computer
Mini PCI-E to PCI-E Wireless Adapter 3 Antenna WiFi Walan For Computer