I, too have the same problem on my 600.
It was a special order, with 384MB, but I wanted to get a 512 and stab it in there and then sell my 256 off to my dad. I couldn't even get the 256 out to test it. I've got little screwdrivers, but none of them would work. The screw in mine is farkin' wedged in there too tight.
I don't know why they couldn't put RAM access on the bottom like the rest of the world does!