You could use an identify by serial number online site to see if your model has
AirPort Extreme card or original (as option) or look up your model in everymac
site to see what specs it shows for the specific actual build model you own.
Mac Serial Number info - Lookup your Apple Serial Number
https://www.powerbookmedic.com/identify-mac-serial.php
Everymac lists all the iMac G4 build models, see them here:
iMac G4/700 (Flat Panel) 700 MHz PowerPC 7441 (G4)
iMac G4/800 (Flat Panel) 800 MHz PowerPC 7445 (G4)
iMac G4/800 17-Inch (Flat Panel) 800 MHz PowerPC 7445 (G4)
iMac G4/800 - X Only (Flat Panel) 800 MHz PowerPC 7445 (G4)
iMac G4/1.0 17-Inch (Flat Panel) 1.0 GHz PowerPC 7445 (G4)
iMac G4/1.0 15-Inch "FP" (USB 2.0) 1.0 GHz PowerPC 7445 (G4)
iMac G4/1.25 17-Inch "FP" (USB 2.0) 1.25 GHz PowerPC 7445 (G4)
iMac G4/1.25 20-Inch "FP" (USB 2.0) 1.25 GHz PowerPC 7445 (G4)
The early iMac G4 (700~800) used Original card, even though iMac G4 17-inch
first model was 800GHz and looked like later build model. ~ Later 1.0GHz were
considered USB2.0 series with 15" 17" & 20" displays; these use Extreme card.
(There two 800MHz models one dual boot, & other not. Both topped out w/Tiger.)
I've owned both types with Original and Extreme cards; a running iMac G4 has
ways in the system or hardware specs to help detail identification.
Good luck & happy computing! 🙂