Search eBay for pci airport. There's a couple of professional sellers there with vast quantities of third-party 802.11g PCI cards that are Airport Extreme compatible. Don't pay more than $30.
I have one in my G5 I bought from
http://stores.ebay.com/the-la-guy - it was cheaper than buying the apple card and totally plug & play. No drivers needed, the system treats it like a regular airport card.
This is a lot cheaper than trying to find an original (and slower) 802.11b Airport card for your Sawtooth.