AFAIK you should not need any special configuration to use the XGP box - the driver should just recognize it. That said, I haven't actually tried it or anything.
What happens when you boot with the box plugged in now ?
Well I got the dual desktop working with Xinerama, but of course Xinerama does not do Desktop Effects, which leads me to believe that the advanced features of the more powerful card are useless, ie playing games.
I tried to use several aticonfig --initial setups, but I am unsure how to get the 'Big Desktop' to work properly. When I do the