If this has been answered before, I'm sorry, I couldn't find any help through searching.

When I Install Debian on a firewire drive connected to a Powerbook5 (TiBook) the installer will not install yaboot to a partition. It crashes when it says it is looking for other operating systems. I have tried with and without mac 10.4 partitions on the drive. I was wondering if anyone could offer any help.

You need to create a Apple_Bootstrap partition and have Yaboot
install there. I can't really help you anymore but to read the
documentations over at Debian.org. If they have any..

The Gentoo documentation for setting up Yaboot on Apple hardware
is here.

thanks, it didn't really help. So far I have no idea how to properly set up a bootstrap.

Well, I managed to set up Yaboot on a super-propertary RS/6000.
That was a real PITA. I used the Gentoo Yaboot instructions
and modified abit for RS/6000.

Do you have 4 partitions? You need that for Apple Newworld:
Apple_partition_map 32KB
Apple_bootstrap 800KB
SWAP
Root

1. start mac-fdisk
2. press 'b' to create a bootstrap partition

More info about that here
There's probably some Debian documentation about this too, but I'm more familiar with gentoo, so the above link was easier for me to find.