I'm not positive on this, but it might be a encryption compatibility problem between your network and your AirPort Card. I believe that OS 10.3.x is only capable of the basic encryption WEP, and not the the more modern encryptions WPA and WPA2. I also think if you upgrade to 10.3.9, that might help get you into WPA encrpytion but it still not up to WPA2 that many modern networks now use. Then there is 40 bit and 128 bit encryption, and I can't help you there with that.
There are two iMacs with a G4 1Ghz chip, the 15" model M9285LL/A or the 17" model M8935LL/A. Both of these are AirPort Extreme ready. Did you use an AirPort card or an AirPort Extreme card? Perhaps this might be a conflict.
There are WiFi protocols like IEEE 802.11a/b/g/n (with each letter signifying a different protocol). I'm pretty sure the original AirPort card on worked on IEEE 802.11a/b. That might be a problem.
I have an old Tangerine iBook running 10.2.8, that I can't use anymore on WiFi because it couldn't handle the encryption.
I hope some of these might be helpful.
Thanks for the reply. I updated the machine to 10.3.9, installed an AirPort Extreme card, and I have tried WEP, WPA, WPA2, and WPAmix encryption and achieved the same results.....
"There was an error joining the selected AirPort network."
If I remove the passphrase security, VOILA, I can connect to the net, but so can everyone else in my neighbourhood.
Any other thoughts?
Ultra Speed is the manufacturer of the router.
I have not contacted my ISP yet because I can get my kid's iMac to connect wirelessly without passphrase security. It's when I add the passphrase that it won't connect. I'm not sure they will be much help. I've contacted the router manufacturer, but we appear to be going in circles with what they have suggested so far.
I've tried everything that has been suggested here and what the router manufacturer suggested, and I still have the same issue. Once I turn passphrase security on, my kids' iMac cannot connect.
Is it that the settings on the router are too new?
Is there a possibly an issue using an AirPort Extreme card in this model of iMac?
Any other suggestions?