Here is a summary of the system:
G4 with AGP Display Adapter
This system used to have 128M of RAM. I bought 2x512MB SDR PC133 RAM from 4allmemory.com --> They've been very patient in replacing the memory twice for us already.
When you have both 512M sticks in the system, it boots up fine the first time, you can check and the system shows 1G of RAM, but when you shut down the system and boot up, it hangs half way as it's loading the icons at the bottom of screen, don't ask which icon, please.
It works fine with 1 memory stick in it, 512MB.
I've tried all the different memory slots. The problem is very consistent in the way I described it happening. It boots up fine the first time with 1G of Ram, but if you shut down and boot up, it hangs half way on loading the icons.