Right now I have Leopard installed to an external hard drive. I use Grub linked to PC_EFI (patched for AMD) to boot Leopard. Now, this works well for a home computer, but it isn't very portable because I have to take Linux (Grub) and PC_EFI with me if I want to run my Leopard. Is there any way I can put PC_EFI on my Leopard drive and have it boot automatically (without Grub), or if that is not possible, is there any other bootloader that I can use.

I don't really know what you are saying but i have a question.
Which DVD are you using?

I apologize. I'm using the Zephyroth 10.5.2 DVD. If I just install it and try to boot to it by using my boot options menu, it wont boot (just displays a flashing cursor). I have to use PC_EFI in order to boot into Leopard. Right now I have PC_EFI on my Linux partition and I have grub pointed to the PC_EFI boot file. I was wondering if there was any way I could transfer PC_EFI to my external hard drive (with leopard on it) and boot to it without GRUB.

Ok so the first question you need to answer is are you using MBR or GUID partition. If it is a GUID partition you can simply load the efi emulator on a small partition on the same drive as leo. If you used MRB it becomes more dificult because you will need to back up the drive and then reformat it to a GUID partition. After that load efi, then install LEO and use the time maching back up you created.

It is partitioned as MBR right now. Is there a way I can boot PC_efi off of a thumb drive instead? I just got everything set up and I hate to go back and format it.

Well, you could install grub to the MBR of your external HDD.
And a tiny ext3 partition to hold the grub files and boot_v8 would not take up much space.