Ya a differential lets one tire move faster then the other so you can turn better in drifting IMO i think u need a limited slip or a locker. a Limited slip makes the tires turn more evenly so when u want to slid the rear u have both tires spinning (not one)and a locker makes the tires spin together so their locked together[8D]

hope this helps

Here are some links:

http://auto.howstuffworks.com/differential3.htm

http://auto.howstuffworks.com/differential8.htm