As far as I know it doesn't work. You can exchange data between two computers, but you can't use it as a router.
But why all that trouble anyway? An airport card for a PowerMac costs 79-99$. For about the same price you get an access point from netgear, that is compatible to airport and has a LAN and a WAN plug. You plug the PowerMac into the LAN plug and the DSL modem into the WAN plug and there you go. The big advantage is, that you don't have to fire up your PowerMac to have access to the internet and it costs you about the same cash...
groovebuster