i fixed my computer this morning!
when i had edited my yaboot.conf i had made a .bak copy but i also just commented out my original file and put new stuff in on top.
i have no idea why, but booting from the ubuntu server cd and using rescue option, then entering the busybox shell it would not let me mount my partitions.
what i ended up doing was just pressing enter and going into the normal installation mode. hitting escape to take me to the main installation menu and then detecting/mounting my cdrom from the options in the menu.
i then selected execute a shell from the main menu when that was finished. note that i couldnt get access to my partitions without first using the detect cdrom option first..
from this shell i was able to mount my root partition on /dev/hda3
i edited my yaboot.conf to its original form
chrooted in but couldnt run the ybin -v -C /etc/yaboot.conf because my boot partition (hda2) and proc file system were not mounted.
i wasnt sure how to mount those so that the ybin command could do its thing, so instead i exited chroot back to the busybox shell and mounted hda2
from there i edited the yaboot.conf in that partition back to its original form and saved. exited the shell and selected abort installation. the computer reboots, loads x and here i am on my newly fixed laptop writing this message.
i'm so happy that i didnt have to do a reinstall!
hope this may help anyone who accidentally screws up their yaboot.conf and needs to get things back running again. it only took me 4 days to figure out.