I think the answer (sort of) to your question is that probably the latest version of Photoshop that will easily run on a G3 machine is probably Photoshop 7. I am not sure what operating system will work on the G3 machines however. As to the RAW files it will read, you don't say what your camera is, but it's not likely that 7 will read RAW files from any Canon camera newer than your G3 machine. I run PS7 quite creditably on a early G4 400MHz desktop (Yikes!-which is to say it is a G4 processor, but the circuitry is the same as the last G3 desktops) with lots of memory, drive space and so on. The same computer will run Photoshop CS, but with some oddnesses*.
I have never tried to run DPP on it although it is installed. This early G4 machine will NOT run OS X Leopard, but it will handle (nicely even) the very most recent version of OS X Tiger (10.4.11). I think this is incredible for a machine I have had since its introduction in 1999. I also run Photoshop CS3 on the last and fastest ever PPC iBook G4 with no difficulty nor, so far as I can see, any problems with DPP, but I hardly ever use the latter. Ditto for a Intel-based Mac Mini, which is a terrific bargain, by the way. Both the iBook G4 and the Intel Mini run OS X Leopard 10.5.4.
Xilisoft movie maker for mac. • Publisher: Anvsoft, Inc.
Paired with a couple of SSD stripe RAID work disks and over 100TB in TB3 RAID 5 this is just a mind blowing setup. On exporting D850 and 60MP Hasselblad raw files in Lightroom 7.2, I just can not work fast enough to keep up with how fast it exports. All operations in LR are incredibly responsive and smooth even using PaletteGear. Mar 1, 2015 - The latest Mac mini is low-priced, but doesn't skimp on power. Day in and day out, and for good reason: They're more powerful. Photoshop and making and editing videos in iMovie, but the Mac mini will do it all slowly.
I think if you want to go to a Mac that will still run the most recent versions of OS and image-editing programs, you will need to get a G4 iBook at least. Do consider buying a new Mini, it's cheap and fast. Get the fastest version with as much memory as can be crammed into it, though. Then buy a cheap 500GB external HD as well. *you cannot double click on a file to load it, it has to be opened from inside PS CS, though all else seems to work as it should. William, as several others have mentioned, you'd be MUCH better off getting a G4 computer than a G3. There are several reasons for this, including faster operating speed.
For one thing, Canon DPP is probably written to run on one of the newer versions of OSX. I don't know which exactly, but I would assume 10.2 or 10.3 would be about the oldest versions that will run DPP. At some point in OSX development, I believe the operating system requires a G4 processor at minimum. What I'm getting at is that if you buy a G3 machine, you may wind up with a computer that will not support a recent enough version of OSX, and may consequently not be able to run DPP. If you're looking for a used Mac due to budgetary constraints, not to worry.
There are TONS of used G4 machines (including iBooks) on the market. -- However, your money would be most wisely and frugally spent on a new Mac mini.
-- I believe the oldest version of Photoshop that will support RAW files is Photoshop 7. However, if I remember correctly, you had to purchase the Camera RAW plugin separately. I don't think it was integral with Photoshop at that point.
Also, that was before the advent of the DNG format, so even if you had the Camera RAW plugin, there's a good chance that you wouldn't be able to edit newer RAW formats anyway. If you're looking for a secondhand version of Photoshop, I'd recommend not getting anything older than CS. (Elements 3 wasn't bad, either. It also included Camera RAW and supported DNG.) Best of luck! I am looking just for the basic editing and storage of RAW files. I understood most of the information above, and now that I have a g3 on the way, I really hope that Photosho Elements 4.0 will be all that I need for the basic editing.