IMac G3 and optical mouse?

It should work. If the G3 iMac has Mac OS 9, you may only have basic one button clicking functionality (no right button or scrollwheel), unless you download and install the Mac OS 9 driver for that mouse (assuming there is one). If it has Mac OS X, you can ususually get the click, right-click, and scrollwheel to work without any special drivers. However, if it has any other buttons or features, you will need to download and install the driver for that mouse.

I use an Apple Pro Optical Mouse with my G3 iMac, and it works great. No additional drivers needed, either for OS 9 or 10.3. I started using the Pro Mouse because I could not stand the ‘hockey puck’ style mouse that came with the machine. I did attach an iCatch to the original USB mouse in order to make it seem like a normal mouse, but still did not like having to deal with the mechanical ball rolling around and getting gunked up. An optical mouse stays much cleaner and is more precise.