I need to find out how to open case on Aspire One d270 so I can replace the memory chip with a 2 GB

Not sure if the d270 is the same as the d255 but you remove the keyboard first .

just above the numbers at about 1  5  8 are little spring loaded clips, its easier to remove the battery and gently bend the plastic back to see them.

once the keyboard is off, there are some screws marked base, about 4 usually, remove these and then at the side of the hdd is a hole push a thin object through it and the bottom pushes off revealing the underside of the laptop.

regards