intel card not working when booting on another VGA card

[strawks]

Hi all,

I have a Gigabyte motherboard (µATX) with an integrated G45 chipset.
I have added an ATI card to play some games.

When I boot on the ATI card (select PEG card first in the bios), I can't
get the intel driver in xorg to display anything.

Xorg sees both cards :
(--) PCI: (0 at 0:2:0) Intel Corporation 4 Series Chipset Integrated
Graphics Controller rev 3, Mem @ 0xe3000000/4194304,
0xc0000000/268435456, I/O @ 0x0000e100/8
(--) PCI: (0 at 0:2:1) Intel Corporation 4 Series Chipset Integrated
Graphics Controller rev 3, Mem @ 0xe3400000/1048576
(--) PCI:*(0 at 1:0:0) ATI Technologies Inc RV670PRO [Radeon HD 3850] rev
0, Mem @ 0xd0000000/268435456, 0xe1000000/65536, I/O @ 0x0000b000/256,
BIOS @ 0x????????/131072

My device section looks like this :
Section "Device"
        Identifier      "Intel GMA X4500HD"
        Driver          "intel"
        BusID           "PCI:0:2:0"
        VendorName      "Intel"
        BoardName       "G45 [Intel GMA X4500HD]"
EndSection

Xorg says :
(EE) intel(0): Bad VBT signature

Fatal server error:
Unknown GTT size value: ffffffff

Note : when booting on the intel card it works perfectly fine with this
same xorg.conf.

Also, with the vesa driver I get an output on the ATI card whether I set
BusID to PCI:0:2:0 or PCI:1:0:0, but a no device detected error when
setting it to anything else.

Any idea on how to make this work when booting on the ATI card?

I have attached verbose Xorg output and my xorg.conf

regards,
strawks

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