Hey,
Ah gotcha...
Ok, well, I've done this before but don't exactly remember how, you'd have to research it a bit... I'm not well versed in Linux either...
But, yes you'd need super user capabilities to edit this file. I believe it's /etc/grub.conf? Not sure. Also, not sure about what exactly you have to add and how it works. But, if I remember correctly, (0,0) would mean that 0 is the primary hard drive, and 0 is the first partition... So basically, an easy way to do this, would be to login as root with your GUI server, then you can edit anything. Or as you said i.e sudo /path-to editor/ /etc/grub.conf and then just add an entry similar to #7 at that website I sent you, but change (hd1,2) to wherever your Haiku and Zeta installs are...
I'm sure you could find better/more correct help on this on a Linux forum though...