Remove your PCI Express video card. At the rear of the PCI Express slot,
there is a small plastic tab that you need to lift up to unlock the PCI
Express card. While doing this, pull gently on the card itself toward you
and it will come free. Set the video card aside.
Immediately to the left of the PCI slots, at the top of the logic board, you
will see this Phillips screw. Using a Phillips P0 screwdriver, remove it.
OWC Multi-Mount
Chapter 2 - Mac Pro 667MHz Disassembly
2 MAC PRO 667MHZ DISASSEMBLY