Booting without Gnome

[Tony]

I am installing Ubuntu PPC Hoary on a Mac Mini.  It appeared to
install correctly, but upon reboot the screen goes blank and I am
getting a message that the frequency of the monitor is out of range. 
Can I boot to a command prompt without initiating Gnome (assuming that
it is an x.org config problem)?

I have tried bringing up a different console using CTRL-ALT-F* but I
get no response.

Thanks,
Tony