i got the same problem with hd 2600 mobile

i booted cd with F8 (then type "-x" flag and ENTER)

you will be able to boot in and install it normaly..

after that if you lucky you will be able to use Leopard normaly, i didn't be able to config my card yeath, so i need -x flag to boot into OS

gl.. and if anyone know how to config hd 2600 mobile, i wold love to know.. ty