first off, why are you using two swap partitions? two distros can use the same swap. just go into your /etc/fstab for the distro that is using the /dev/hda7 swap and change the entry that looks something like
/dev/hda7 none swap sw 0 0
to refer to /dev/hda4 (I'm assuming you want to use the bigger swap partition), then you can use that other swap space for something else.
secondly, it looks like the ubuntu installer has already set up an entry for debian in the boot loader.
# This entry automatically added by the Ubuntu installer for an existing
# Linux installation on /dev/hda3.
maybe the boot loader is like the one in fedora, which just boots the default OS unless you press a key within 3 seconds, at which point it comes up with the boot menu.
I'm not familiar with yaboot, but "man yaboot" should turn up how you can turn this functionality off, if indeed this is whats happening.
if this isn't whats happening, what *exactly* happens when you boot?
also, this might help you: http://penguinppc.org/bootloaders/ya...t-howto.shtml/