Wait guys. We are recommending he buys a pentium dual core. According to him he already has one. Let's make sure of what he's got before we recommend something else. He says hes got a pentium dual core 3.0 ghz, in which case would be a pretty nice cpu.
If so, grab like 2-4 gigs of I assume pc6400 ram, maybe a new psu, and you have a nice cheap build.
Edit: You said you are for sure going to get the e8400. Just take a minute and make sure you don't have a pentium d x2 at 3.0 ghz, because if so I don't think the money you are going to spend would be worth the not so huge improvement.