MoreIchatEffects is a collection of 56 effects for iChat on SnowLeopard and Leopard.
These effects are available for G5 and Intel processor.
Some are supported by PowerPC G4 with Powerboost to add support of the simple effects on your G4. "Cack-drop effects" will still be unavailable for G4 and G5.
If you want to remove all effects, run the installer or remove files in /Library/Compositions