It should, three things to know. First, all 3 will run at the speed of the slowest ram. Second, watch the voltages if they aren't the same. You don't want to cook one chip to run with the others. Third, adding a 3rd chip will have all 3 run in single channel mode, lowering performance a little.
if they run in single channel mode will that lower the performace so much there wont be any point running the 3gb?