Here is mine. Don't hold mine up on a pedestal though, plenty of mistakes made along the way... Look thru the forum for others mods to give you some more ideas.
And not only do I have OSX running, I have it running in a Virtual Machine - just goes to show that it can be done, if you have the time, energy, and resources. I have 10.6.8 and 10.8.2 running in 2 different virtual machines.
I reused none of the actual electrical parts. Others have reused the fans, or modified them in various ways. I replaced them because the old ones draw a lot of power, make a lot of noise, and don't cool as well as cheap 5 dollar fans. you just cant reuse the PSU. I tried and tried, but it just doesn't have the right voltages, amps, and distribution to run an modern ATX motherboard. I did reuse the fan mounts and the PSU case. Cosmetically, the G5 looks the same... I upgraded all the good bits to new stuff though.