Currently I'm using an iMacG4 800Mhz with OSX 10.4.11 (the max OS it can use). While it's fine for most browsing on the net, you can't watch things like youtube videos on it properly, it only displays a pic about every half second or so.
Strange, because it can play DVD movies with any problems. I wouldn't use it for anything else other than the net, as my 060/ppc amiga can edit JPegs and gfx quicker using ImageFX. In fact trying to do most things on it is just way too slow and can be done more easily on my amiga.
I don't know if the OS versions were all basically the same, but to find the processor speed on this one, all you do is go to the apple menu and select about this mac then info.
Unless you can buy a mac with at least a G5 in it, I wouldn't recommend it for anything other than a net browser, they are just too slow and flakey for anything else...
To find out all the details about any old mac ever made go here...
http://www.everymac.com/systems/apple/
