Which version of Mobility Radeon?
It needs the legacy driver from ATI and I'm not sure if there is one that EnvyNG does not know about
Seems that you can forget the ATI drivers and must rely on the open source drivers
What I think has happened is that you got the "vesa" driver while it should use the "radeon" driver
Check /etc/X11/xorg.conf
There is only one Section Device and it should look something like
If it say vesa change it, if it says something other than radeon or vesa please tell usSection "Device"
Identifier "Configured Video Device"
Driver "radeon"
EndSection