The mouse will work without anything special. It is a standard USB mouse and should even work with a PC. This goes for the keyboard, as well, except for the volume up, volume down, mute, and eject keys. For these to work you will need to copy over the USB Device Extension that came with the iMac (either version 1.4.3, 1.4.4 or 1.4.5, depending who you ask). This should work perfectly well, although Apple doesn't support it. They will most likely release an updater with the newer USB extensions, since many people's Pro Keyboards have now shipped. It could also be part of 9.1.
This is what came with a Summer 2000 (Gigabit Ethernet) G4. I would guess the iMac's software is similar.
The only new thing in the Mouse Control Panel is that it has pictures of a Pro Mouse instead of a hockey puck mouse.
The Keyboard Control Panel has been updated to use all 15 of the Pro Keyboard's function keys (for Hot Keys). The Sound Control Panel has a new interface with tabs, and a gain slider and level meteor in the "Input" section. Also, there is Open Transport 2.6.3, OpenGL 1.1.5, ATI 3D Accelerator 5.0 (along with other updated ATI extensions, including a Radeon driver), Apple CD/DVD Driver 1.3.9, Apple Audio Extension 1.1, FireWire 2.6, Apple DVD Player 2.2.1, AppleCD Audio Player 2.5, DigitalColor Meter 2.0, Monitors 8.6, Energy Saver 3.0, Drive Setup 2.0.2, updated DNS/SLP/LDAP plugins, and a few updated Control Strip modules.
[This message has been edited by mkincaid (edited 09-26-2000).]