question 1: i'm trying to open up the latch on my powerbook's g4 1.67 memory. the screw in the bottom right corner came off no problem, but the others will not budge at all. what's going on? question 2: i have 512 mb in one slot and nothing in the other. is it okay to get 1gb in one and keep 512 in the other or should they be identical for optimum use?