What can I upgrade to? Do I have to start with os 9 or can I go to panther? when I install os 9 it ask for an air port which I don't have so I skip that part and it installed but, fail to see the internal modem.

I have a G3 IMac with Os 8.6. I'm trying get on the internet with the internal modem, when I try to dial up or conect to earthlink all I get is a busy signal.