Install OSX on External HDD with Bad internal Controller

[ElectronicsGeek]

I am attempting to install OSX on a external HDD . Now please excuse my ignorance. The internal controller is definitely bad. I pulled out the hard drive and successfully booted from my external controller. I decided to to get rid of everything on my disk with My Ubuntu machine by just deleting the partitions. I then used the original DVDs and attempted to boot holding c . It reads the DVDs and boots up and says os 10.5.5 can not be installed on this computer. I created one large 160gb partition. Am I missing something or should I be adding a small fat partition. Not sure what is going on thanks for any help!