Im guessing your using a socket 775 right now becuase you have an E2200, i could be mistaken but i highly doubt it considering its a core 2 duo and they are all socket 775.........if you were to upgrade, you could get any Quad series from intel, just not the new i7 or i5 CPU's. I have a Q6600 which is stock 2.4ghz but i overclocked it to 3.65ghz.
What makes a CPU good is the clock speed, cache, bus, and cores. In the case of intel, the new i7 have virtually 8 cores becuase of hyperthreading.
If your gonna build a new computer and wanna know bout CPU, from intel if you have a decent-high budget get an i7, they are hte fastest out there. If your on a a budget, either get an i5 from intel or an AMD phenom II, i recommend intel though cuz they are faster so far. You need to get compatible motherboard and a decent power supply so it can atleast power a decent graphics card.
Q9550 (This thing is pretty fast cuz of the large cache and is actually faster than the new AMD phenom II in most cases + its running at a lower clock which is all the better) -
http://www.newegg.com/Product/Product.aspx?Item=N82E16819115041
i5 750 (Cheaper than a Q9550 but would require an entire upgrade) -
http://www.newegg.com/Product/Product.aspx?Item=N82E16819115041
i7 920 (This thing is fast and will last quite a while, especially if you overclock to around 4.0 ghz) -
http://www.newegg.com/Product/Product.aspx?Item=N82E16819115202