the one you have at the moment is better. The one you have is a core 2 duo whilst the other one isn't.
1. I have a new hard drive.what are you full specs?
If things are getting a bit slow how about upgrading the ram or degfragging the hard drive.
I'm buying this one will it fit on my motherboard its a E8400getting an E8400 or E8500 would really ratchet things up for you; do some ebay hunting for a good deal on a used cpu