I got an ASUS M3A78-CM motherboard recently when upgrading my Debian Linux box (Lenny).

I had some trouble getting the "radeon" driver to detect the card, which showed up in `lspci` as follows:

01:05.0 VGA compatible controller: ATI Technologies Inc Unknown device 9611

I had to add the BusID to /etc/X11/xorg.conf, in the "Device" section:

Section "Device"
        Identifier      "Radeon VGA port"
        Driver          "radeon"
        BusID           "PCI:1:5:0"
        Option "SWcursor" "true"
EndSection

After which time, it detected ok.