Not the Video Card
I finally got fed up with the hanging and crashing on the AMD64 with the GeForce 6600, so I swapped them.
I figured that the extra video processor on the 6600 in the P4 (2.4GHz) would be a boost, and the 5600 in the AMD64 3000+ (2.0GHz) would benefit from the extra CPU.
I restarted the P4 first (just put it together in that order), and tried Savage which kicked out 120FPS. Sweet; with the 5600 I peaked at 85FPS. There were still lag hiccups, but I figured that was fairly normal. No blittering graphic anomalies, no seizes due to lag, and nothing else out of the ordinary.
I restarted the AMD64, and it buzzed up, too. The resolution was still set to 1280x1024, and for some reason Ubuntu wouldn't let me change to 1600x1200 (but I'll fix that later). I kicked on Savage, and got the 85FPS that I think is pushing the limits of the 5600, and for the first time, no seizes during lag! However, there were still the blittering elements that cause occasional random polygons to be misdrawn. I'm gonna start blaming my (now) POS mobo; the MachSpeed K8M8MS. Time to look at an ASUS or MSI, I guess. Maybe this guy will make a good upgrade to the Solaris box running on a 366MHz Celeron...