both are fairly old
both are fairly old, however the pentium d is simply a dual core pentium 4. so the athlon is better here.
what are the clockspeeds of both?
Here is comparison between X2 250 and E6300
http://www.anandtech.com/bench/default.aspx?p=94&p2=96
(Note: in some benchmarks lower means better, so read each one carefully)