If you intent to run a 3D game at, say, 1024*768, then NO, you won't notice a difference.
At resolutions of 1024*768 and above the graphics card is the main component defining the speed. There's a hilarious benchmark at Tom's that shows that.
So if you're going to buy CPU for gaming, buy the cheaper Duron, and use the money you saved to get a better card. Or alternatively, buy a cheap Duron AND a cheap card and get a upgrade on both in half a year...