If you decide to use this solution, BE CAREFUL and invite an Electrical Engineering friend over to check your work. The PSU sits completely flush against the bottom of the case and looks really good! I sacrificed on SATA power cable to power the original PSU fans (tiny 40 or 60mm fans towards the front). I didn't like the look of this and disassembled my ATX supply and transferred the electronics into the original G5 PSU enclosure. Unfortunately there is not a great way to secure an ATX supply to the bottom of the case without drilling special holes. BE CAREFUL! The easiest way is to remove JUST the power connector, glue it to the inside of the case, snip a spare power cable and wire your ATX supply to it. If you want to use the original power plug you need to take this apart. The original PSU is shorter and longer than an ATX supply and fills the bottom of the case. Replace the old IDE drive with a modern SATA one. Reinstall just what you need to to mount the drive. Cut it shorter with a hack saw right where the 5.25in drive mounts end.
DUAL CPU MOTHERBOARD IN A POWER MAC G5 CASE INSTALL
You need to remove this piece to install the motherboard tray. By default it's mounted to this piece of sheet metal that runs the length of the case, parallel to the floor, dividing top quarter-ish of the case from the bottom. The CD/DVD Drive flippy-door-action is one of the coolest parts of this case. Also, unless your motherboard has FireWire header (probably doesn't), the FireWire port won't work, just FYI. You can find wiring diagrams for this online. Making a cable isn't difficult but requires some time and tools. The original front I/O cable will NOT work with an ATX motherboard. Make sure you use an INVERTED motherboard tray! Take a look at the G5, the removable side panel is on the other side of the case.(the motherboard will be "upside-down"). My current PC case is a G5 and I love it!