A "disk image" is NOT necessarily the same as an ISO. An ISO will specifically be a .iso file - that's not a Windows / Mac / Linux file format, it's a universal DVD format. As long as it's called "DVDIMAGE.ISO" or "WE8.ISO" or something, it's fine. You just need to select the option in whichever burning program you use that says "Burn ISO image", and if there's an option for it, select "disk-at-once" or "DAO" mode. You must burn in DAO mode so you get a disc burnt in PS2 format, instead of just a data DVD with a lot of PS2 files on it, which won't load, if you see what I mean. If there's no option for DAO, but you're definitely in 'burn ISO image' mode, it should just be set as default (like in DVD Decrypter).
I use Linux for all my patching, and it works fine. All the patching tools are pretty simple programs, so they all work perfectly under WINE, the Windows emulator for Linux. There are definitely similar sorts of emulators for Mac, as a friend of mine patched WE8 with ppf-o-matic on his I-Book. There will be at least one that's free, if you search. As for burning -- search for freeware Mac burning programs! Or a Mac port of a Linux program like k3b, which is really easy to use.
Only thing that doesn't work properly in Linux is Waterloo's tool, cos it needs specific Windows libraries, so it won't work in Mac either. You could fix that (by placing the .dlls you download with the new Waterloo tool in a specific folder in the 'fake windows' environment), but I can't be bothered -- I just boot into Windows for that
