If you're really curious, it wouldn't hurt to pop that sucker in and try it out. You can always take it out if you don't like the results!
But since you don't have to make a financial decision, giving it a shot and seeing the results first hand will be better than any speculations any of us can make!
Very good advice from ForYourHealth ^.
HD2000 is considered comparable to a $50 graphics card. It might actually be better than the 8400GS(a $30 card)
If you are running well, why bother messing with it.
If you are short of ram, then add more; ram is cheap.