Re: Driver 962x and DGA issues ...
There's a known bug in 1.0-9629 where X will crash when certain types of mode changes occur (such as starting Doom) while using a DFP. This bug has no association with DGA, as there is no DGA support in the nvidia driver going back several versions (this is documented in the driver README as well). This bug will be resolved in the next driver release. The current workarounds are to either change to the desired mode using xrandr, or downgrade to an older driver version.
As for the Compiz/AIGLX/Composite issue, the Composite extension is enabled by default in FC6. If the Composite extension is failing to load, this suggests some other problem with your environment as you are the first person to report a problem such as this. Additionally, I'm running FC6 on the system where I'm typing this, as Composite is loaded with the 1.0-9629 driver.