Desktops :: Setting Up Replacement G4 Mirror Door Model

My much loved G4, dual 1GHZ processor, mirrored door model, finally died. I bought a second hand G4 with the model spec just below this one - the 867 MHz processor - as I wanted to go on using my cinema display monitor with ADC connector. Newer MACs won't run this monitor without a special adaptor box (which costs more than buying a second hand G4!) The G4 I bought doesn't have a DVD-RW drive, just a CD drive. I had a DVD-RW drive on my own old machine. I was wondering - is it easy to take this drive out of my machine and put it in the one I bought? Or does the lower spec make this a problem?

The guy I bought the G4 from had looked after it well, added a second large hard drive, and updated to Leopard. I had still been using Panther on my own G4, as I still needed to use Classic for some software and games. So, second query is - can I easily reinstall the OS on the MAC I bought to go back to using Panther? Or is there a way to run both operating systems, leaving Leopard as it is - very useful to have for some new applications - and installing the Panther OS on the other hard disc? Ideally, I would like to have both available, but if not possible, then Panther use would take priority. I have the Panther install discs, but the G4 I bought did not come with Leopard install discs.