The LGA775 socket (ie. C2D) is a dead-end path. You would need to look at the Intel Core i3/i5/i7 chips, or an AM3 offering.
I would go with an AMD Athlon II X4 + 890GX motherboard
The Intel i3-530 + H55 motherboard.
Either would be fine, though the AMD path would allow for better future upgradeability.
4GB RAM is the standard these days, to be honest the best value is in the 2x2GB kits.