Don't think the XW4300 can support the Core 2 DUO, says it supports the pentium D at the max. Anyways the XW4400 supports core 2 duo so I believe this is a motherboard compatibility issue. Apart from that I don't think its worth the upgrade, you should try and do a makeover and start a new build from scratch given you have the money.
Thank you for your help.
I also want to know which pentium d is going to give off the least amount of heat. And should I get regular pentium d or pentium d extreme edition