Please help

[cow1970]

Hi,

Have a IMAC 2008 model and this has snow leopard as the os.
I have an external firewire drive and have just installed linux mint to it.
However I can now no longer start any os on this computer think I may have removed the boot loader from osx by mistake.
I get a progress bar on start up and then a spinning grey circle which does not go away.
I cannot boot via mac osx start disc as my internal drive is broken.
I cannot boot from my external dvd drive.
I cannot enter safe mode or reset pvram.
Am I screwed? Can anyone help?
Hopefully
Matthew