You'll need a new motherboard, so read this thread...
http://forums.anandtech.com/showthread.php?t=265026
this. the e6300 c2d is way lower clocked, you would definitely notice a difference going to the athlon 2You should see a good jump in performance if everything is stock. We're talking close to a 1Ghz clock increase on 2 processors that perform about the same clock for clock.