Never bootloaded before and I tried it tonight.
I am using an UNO as a programmer and all seems to go well until I use the Burn Bootloader w/ Arduino as ISP
Returned error is
Expected signature for ATMEGA644P is 1E 96 OA
Double check chip, or use -F to override this check.
I am using a ATMEGA644PU. Is this different from a 644P?
It looks like you have got a quite different MCU than you try to program.
You should try to program it through avrdude and type -p m644pu or some different atmega644 instead m644p if you are sure you are not using 644p.