I need to upgrade from 256mb to 512mb in my Toshiba Satellite 1005-S157. I need the 144-pin SODIMM SDR PC133 sticks, specifically. Is there a reason to replace the 1 256mb stick that the computer came w/ and get 2 new, or would adding just the 1 stick give me the same boost. Is a name brand RAM better by a noticable amount? Also, are there any compatability issues between brands?