There might be, provided you're iBook is running Mac OS X.
The G3's only support USB 1.1, though, so you won't get super fast download speeds (but that's not really the point
)
If you want WPA2, I think you need to be running 10.4.11. Not super positive, though.
For OS 9, ianj is correct. There is no software that will allow you to use generic Wireless G WiFi cards/dongles with WPA/WPA2 support. Not yet, anyway (it's not within the realm of impossibility that someone will eventually figure out a way to implement this functionality, so it could very well become a thing).
c