You can use the alternate install iso for now.
The card should be supported, it is possible though that it is not being recognized correctly. You might have to manually configure the x-server. I don't know if you can boot to runlevel 3 witht the ubuntu live cd, so the alternate cd might be your best shot.
It should work with the flgrx driver. I don't know if it is being installed by default.
You might have to configure the x-server manually: