Newer machines are quite a bit faster than that unit. P4-M processors are very inefficient compared to Pentium M or Core-based machines. Your memory amount is good, although the memory speed is likely low given the probable chipset. The video card is a huge deal; a 64mb GeForce 440 card is "terrible" by today's standards, so newer machines with dedicated video chipsets will yield very large speed and quality increases over the board.
I think you're at an interesting position. It really depends on what you're playing. If you're playing games a couple years old, then your machine is sound...don't fix what's not broken. But if you're wanting to play some of the newer releases, then a new machine is a very good investment, possibly even crucial depending on the game title and minimum specs.