What socket goes to a 2.0 GHz Intel Core 2 Duo processor?

Assuming this is the Intel® Core™2 Duo Processor E4400
(2M Cache, 2.00 GHz, 800 MHz FSB), the socket is LGA775:

http://ark.intel.com/Product.aspx?id=29753&processor=E4400&spec-codes=SLA3F,SLA98

You can use http://ark.intel.com/ to lookup socket and other product information on any Intel processors