I have the 13" mbp. My friend bought the wrong kind of RAM and was going to sell it to me (it'll work in the mbp). I've only ever had either 1 stick of RAM or two sticks of the same amount in the two other mac laptops I've owned previously. Right now I have two 1GB sticks, can I take one out and put in a 2GB stick? I'll end up with a 1GB stick that it came with and this new 2GB stick for a total of 3GB. Is there anything wrong with this or should I go out and buy a second stick of the RAM my friend is selling me?