Although a faster processor always helps, but it is the sum of all parts that will make your game play or enjoyable. Upgrade the processor to T2500 or better. Have 2GB of 667 RAM and the X1600 Video card. Even this won't compete with the top of the line gaming systems, but it should satisfy your thirst, at least on a laptop.
Do a search for SUCKA. He upgraded his laptop and provided pictures. He even upgraded to a Merom chip and said there was a 20% increase in speed.