what is your price range? i3 2100 system would cost you about £350 (sorry, dont know dollar equivalent) at the most. E6400 system would only cost you around £300 at most.
E6400 is about half as fast as i3-2100. The platform would not be upgradable and you would have to buy DDR2 which is more expensive than DDR3. Unless you get one of those strange s775 boards that takes DDR3, which would be just dumb imo.
For $200 USD you can get i3-2120, 8gb ddr3, and a H61 motherboard.