If you want to upgrade this machine to OS X, you will of course need to secure a set of install disks. Apple used to sell Tiger disks along with Leopard for a little while, but they no longer offer that on their online store. I suggest ordering some on Amazon or eBay, etc. Tiger should work fine on this machine. When you get a copy of OS X, you can either: completely wipe the drive and install a clean system, or create a partition on the drive and have the option of dual-booting OS 9 and OS X. If you don't need or want OS 9, you could go ahead and wipe I suppose; Classic should work well enough for anything you may need it for.
You may want to just buy a larger hard drive and turn the 40GB HD into extra storage. Power Mac G4s have at least two drive bays if I remember right. Once you have OS X disks, all you need to decide is how you want to upgrade and use the machine. Good luck.
I was given a Power Mac G4 model 8493 733 MHZ Machine ID 406 with a 9.2 os. I upgrade the ram to 1.1 GB of ram from the original 128 MB. the hd is 40g. What I like to know is how to proceed and where to obtain a newer OS.Without involving to much money.This unit is just like new.I already own a Macbook and Imac24" that are less than a year old. The Power Mac is more like a chalenge to me and something to keep me busy. I would appreciate any help and advise that can be given.