After a nightmarish 24 hours, I've successfully installed Ubuntu 10.04 x86-64 Server on an HP ProLiant DL580 G5 server with an added P800 Raid Controller device. I wanted to make a public record on the steps to finish the installation in case it helps anyone in the future.
The issue we were running in to was the message "Illegal Opcode" given after BIOS startup before the OS could load, even after a successful OS installation. HP support confirmed that this message is given when the MBR on the boot controller does not refer to a valid bootable partition.