can I upgrade my dell dimension e520 with a pentium d 805 2.66 ghz to a intel dual core e5400 2.7ghz wolfdale 45nm processor

I read on the internet that the 45nm processors are not supported but on the dell chat the person was trying to sell me a wolfdale. I thought I should go for a 2nd opinion.

what processor would you suggest if the 5400 is not compatible?