Greetings!
Just as Patio says, we need a little more information about the machine. GRanted it is a Core 2 Duo, one can assume its DDR2.
HOWEVER there where some machines that had core 2 Duo's that did indeed have DDR3 1066Mhz. Granted these are rare, but you need to be sure so that you dont do any damage to the board or the RAM.
Please offer us the model number of the board and or manufacturer and model number of the computer if it is a name brand. Ie (Acer, HP, Asus, Toshiba...etc)