How to boot Mac from CD from verbose command line

So already I've tried booting Ubuntu on a USB from the Mac's command line (verboes or something like that). But it didn't seem to work at all and said load size is too small or came up with a no entry symbol. So I put a Ubuntu 32 bit on a CD and now I don't know how to boot it. I can't open up the boot menu as all of the important drivers are gone from the computer.