I've put extensive research into the subject of fitting a Mini in an iMac G4. To be brief, the Mini will fit in the iMac (though I'd take it out of the case to get better ventilation) and with the proper adapters you can use a desktop sized hard drive and optical drive with the Mini. The only catch is the display which uses an irregular connector (there might be an adapter for it, but I don't know the type of connection). My thoughts on this hindrance would be to essentially buy a DVI display, remove the casing, and the somehow mount that in the display housing of the iMac and feed the power and DVI connector through the neck. Good luck though, it won't be an easy task.