DDR2 RAM can be replaced with DDR3 as they both have the same
pin configuration, however this doesn't mean that your machine
will neccesarily run faster due to the fact that it will rely
on the serial bus width of your motherboard (I think!
Sorry I was pulling that comment off the top of my head.
Pretty sure it's front side bus which will determine the ammount
of memory a system can handle (or should I say address)