I found an old macpro 2,1 and wanted to get esxi 5.1 on it as a backup incase my xserve dies. I started with a unetbootn esxi 5.1 USB, that freezes. So I took that bootia32.efi previously posted and put it /efi/boot (overwriting the old). That got the installer to boot and install to disk no problem. When it rebooted its now the same old problem again.
So then after some trial and error, lots of error, I came to this final solution. Enjoy.
Here are the final steps I took to get it working. You need two flash drives and a blank dvd. My flash drive is H: on windows and it's label is TINYRED:
Preperation:
1. burn ubuntu mac dvd
http://releases.ubuntu.com/quantal/ubuntu-12.10-desktop-amd64+mac.iso
This is a special cd that boots on my macpro at least. The regular cd wouldn't boot.
2. make esxi installer usb (5.1 current) using unetbootin for the esxi installer usb.
copy BOOTIA32.EFI to H:\EFI\BOOT
3. make usb with the good files from the old version of esxi that I've attached. I downloaded VMware-VMvisor-Installer-5.0.0-381646.x86_64.iso from some scandelous website, installed it, and then booted ubuntu just to strip the /efi/boot and /efi/vmware folders.
plugin usb esxi installer to macpro
boot into usb
install esxi to local harddrive
reboot to ubuntu mac cd
open terminal
sudo mkdir /mnt/sexi
sudo mkdir /mnt/usb
sudo mount /dev/disk/by-label/ESXi /mnt/sexi
sudo mount /dev/disk/by-label/TINYRED /mnt/usb
sudo cp /mnt/usb/EFI-BOOT/* /mnt/sexi/efi/boot/
sudo cp /mnt/usb/EFI-VMWARE/* /mnt/sexi/efi/vmware/
take out the cd, remove the usb, and boot into vmware 5.1! It will hang on the white screen for 10 seconds or so, just wait for it.