Somebody from the 'how to' video said Acer One ZG5 can only take a max of 1.5Gb memory. It comes with a 512mb onboard memory and another 512 on the single memory expansion slot making up the total memory of 1Gb.
You can replace this 512 mb DDR2 SoDIMM with a 1Gb DDR2 on the slot underneath the keyboard/motherboard to get to a max of 1.5Gb. I tried to put a 2Gb DDR2 but the system just had a .single light and did not response/froze.
I have opened my Acer One three times to find this out by following this video and only needed to remove an additional three screws on the right side of the motherboard.. next to the hard disk so that I can slide the whole motherboard out/towards you to get underneath it..