OS X :: Migration Assistant Will Not Recognize Old Computer?

I have recently purchased a 24" intel iMac (latest revision) running Mac OSX 10.5.6. I tried to transfer the user account from an older computer upon initial startup using the built-in migration feature, but it failed and reported that "there are no versions of mac os x available on your old mac," which is obviously not the case, as I am trying to transfer from an old white PowerPC iMac (with the hemisphere swivel base) running Mac OSX 10.4.11. All the correct procedures were followed using a firewire 400 to 800 cable.

I then found somewhere that it is wise to try to create an account on the new computer and then try to use migration assistant to transfer the account. I tried this several times, and every time the new computer did not recognize the older mac, and just left it searching (all the correct procedures, such as holding down the T key during restart on the old computer, were followed. The old computer has the firewire symbol floating around on the screen as it should).

I also tried the network option, where the new computer gives a number to type into the old computer, thereby linking the computers. This also was unsuccessful and just reported that a network error occurred.

On one of my latest firewire attempts I was given a message on the new computer that stated "Your old mac might not be able to connect to this one using Firewire" What?

Does this mean I'm screwed? How do I transfer my old account to my new computer? Please let me know if you need additional information on the situation.