I use an Atheros card on my laptop and it's well supported, however you do need to have the Madwifi drivers installed. This thread
on another forum may give you some further assistance. You should be able to install Madwifi via yum if it is not already installed. The Realtek 8169 also seems like a well supported chipset so it should be detected -- what does "ifconfig -a" (no quotes) run as root from the command line show?
Also, Fedora 6 is no longer the latest version -- you may wish to upgrade to 7. In general, the later the release the better the hardware detection/compatibility.