Comment 56 for bug 56692

New driver should use higher agp mode by default, you can enable it with "Option" "AGPMode" "4" manually, but it's unlikely to make a lot of performance difference. When you see those fallback messages for things not implemented, software rasterizer is used so it's expected that performance is very low and cpu usage at 100%. Not sure why cpu usage is quite high even when hw rendering is used, maybe it's just state overhead or vertex submitting or something not very well optimized - you could use oprofile to get a rough idea.
compiz should run better with current ddx and dri drivers.
The google earth gpu lockup (maybe - you didn't say if the box is truly dead or it just appears to be dead) could (or not, I don't know but it would be worth a try) be fixed by a newer dri (mesa) driver.