an internal wifi card was optional.
You need a USN wifi stict that is compatible with your Mac. This one shuld work
Supports Windows , ME, 2000, XP, vista , windows 7,MAC OS 10.X, Linux
Just mak sure that what yo get works with OSX 10.4.11 or 10.5.8. Your G4 Mini can only go to 10.5.8