Samsung have taken the wraps off of the industry's smallest 2GB DDR3 memory chips, built using 50nm processes, which allows for 60-percent higher productivity than DDR2 chips of an equivalent density.
In Windows you generally get more of a boost out of additional RAM than you do out of dual-channel. That's not to say that dual is bad - per the earlier posts, if the OP has 2x 2GB and just got a ...