I don't know what kexts are included in the flash boot, but apparently at least one of those you were using in the previously install is not on your boot drive. I would suggest trying Tonymacx's [url="http://www.insanelymac.com/forum/topic/279450-why-insanelymac-does-not-support-tonymacx86/"]#####[/url] disk for ATI. I have used his Nvidia version to boot a couple of my installs. You can use DD's script to do the install no matter what you use to boot the machine with - the important thing is to find something that will boot.
FYI - got the boot flash drive working with this card. I guess I needed to add EVOEnabler and LegacyATI4800Controller.kext to the boot_disk/extra/extensions folder.
Now I got stuck on booting the 2nd time to copy the script over to the main drive. As I was installing the first time, I saw out of the corner of my eye a black sreeen flash with text, then got a reboot. The flash drive only gave me the option of installing so I am thinking it crashed during the first install? If it fails again, I might try the ATI_Init.kext and try again.
Ah! I got it. It wasn't clear to me from the instructions... after install, boot from the flash drive, and once you are at the bootloader screen select the hdd you just installed to. Copy the script from there and proceed...