Thanks to you both, I was able to finish Riven--I replayed it, and aside from a few glitches (the computer kept my old saves from the first try which was a bit confusing, and I had firedome code problems but had saved Gehn's journal so eventually the slider code worked).
On to Exile (3), after I reconfigure the dual G5. I played 3, 4, and 5 in, I think, 2008. Have to buy 5 again, and I believe it's the one where you have to "draw" on some tablet gizmos which drove me batty--I have a slight hand tremor, but I refuse to give in to the fact that I'm no youngster.
Thanks for the info on available Mac games. Wish there were more of them. Maybe I'll give in and get an inexpensive PC and see whether I can master it.
You both were absolutely stellar in your help for me--I am so impressed with your sticking with my Riven journey. Many, many thanks.