Airport 802.11g for older iMac

Just got an iMac G4/800 that needs an Airport card, however I'm aware the original Apple one is 802.11b only. Apple mentions on their site that certain third-party cards will work, but they don't seem to specify if these cards are for the Airport slot or USB. Are there 802.11g cards that fit in the Airport slot?

I was in the same boat looking to get an old G4 to hook up wirelessly. I bought a usb dongle that went into the usb port and unbelievably it works flawlessly. It's fast and I did not have to put in a airport extreme wifi card at all. Go to Afterthemac.com and you can do what I did and chat online to the tech's. Tell them what system you have and you will probably end up buying the same one I did. Cost around $55 and took 5 mins or less to install.