I wasn't sure which thread to post it in so I decided this one because more people are looking at it. So I upgraded the RAM in my 2009 MBP from 4GB to 8GB. It is DDR3 1066 MHz. My brother has an old MacBook with 2 GB of DDR2 667 MHz. Would I be able to put my old 4GB DDR3 in his computer? Would this cause any problems? Would the computer just underclock my RAM to 667 and keep everything working fine? Thanks!