2) Supreme Commander ALSO fails, in exactly the same way.
So. Not fallout specific. I begin to wonder if it's the card.
The ATI Radeon X1900 is a dual-width card sitting in slot 1. I've got an HD 2600 sitting in slot 4. I won't put the 1900 anywhere else, because it's dual width and it would have to be in 2 or 3 and could only run at 4x (currently it's at 16x and the 2600 is at 8x). So, what I'm thinking I might do is replace the 1900 altogether, keep the 2600 as the secondary card, and put something newer and nicer in slot 1 to be primary.
Apple's online store only sells video cards for Early 2008 or newer Mac Pros. Arc is an Early 2007 (the first 8-core model, introduced Apr 2007, ended Jan 2008). So, I can't tell if they would work with Arc (they specify compatibility by model and memory speed, and all want faster than Arc's got). So, I can't buy one from them.
Went to Fry's, to see what they had. They've got lots of things, but they sell no video cards for Macs. I stupidly neglected to ask what they have that supports EFI, since that's what it needs to work in a mac, and I suspect if it doesn't have a big flashing sign saying "MADE FOR MAC" they wouldn't realize it's mac-compatible.
By the time I was done there it was too late to go to the apple store in the mall. Maybe I'll go tomorrow or something, see what they suggest.
In the mean time, I've cleaned out the heat sinks on both video cards, and will experiment to see if maybe that helps the problem any. I am not hopeful.