For troubleshooting purposes on two videocards I use isolatedevice on one of my primary video card. And nothing else to my aticonfig --initial
Note I have two cards in machine, but I want it to pretend like theres only one. So I would of thought that when u use IsolateDevice that it would prevent the os from looking for another card. But when i use it not only does it seek out the card still, but fails loading it correctly. Any ideas?
Section "ServerLayout"
	Identifier     "aticonfig Layout"
	Screen      0  "aticonfig-Screen[0]-0" 0 0
 	Option "IsolateDevice" "PCI:1:0:0"
        Option         "AutoAddDevices" "off"
	 # This option disables VGA and VBE calls on IRQ 10, to avoid
        # calls for a card interfering with the others.  See also the
        # file "xorg.conf.probe".
#        Option          "NoInt10"       "Yes"

Section "Device"
	Identifier  "aticonfig-Device[0]-0"
	Driver      "fglrx"
	BusID       "PCI:1:0:0"
	ChipID       0x95C5