Is there a reason you're running 10.4.2 instead of the much later 10.4.11 ?
What security/encryption are you using now, & what would you like to go to?
So we know more about it...
At the Apple Icon at top left>About this Mac, then click on More Info, then click on Hardware> and report this upto but not including the Serial#...
Model Name: eMac
Model Identifier: PowerMac6,4
Processor Name: PowerPC G4 (1.2)
Processor Speed: 1.42 GHz
Number Of CPUs: 1
L2 Cache (per CPU): 512 KB
Memory: 2 GB
Bus Speed: 167 MHz
Boot ROM Version: 4.9.2f1
Then in Network>Aiport card report this...
AirPort Card Information:
Wireless Card Type: AirPort Extreme (0x14E4, 0x4318)
Wireless Card Locale: USA
Wireless Card Firmware Version: Broadcom BCM43xx 1.0 (220.127.116.11)
Current Wireless Network: AispWork1.3
Wireless Channel: 11