How do I find out what size socket my processor is?also I have a single core processor will changing to a.....

dual core effect it? this is the processor I want tell me if its a good deal also can someone please tell me how to install a new processor. AMD Athlon 64 X2 5200+ Processor ADO5200DOBOX - 2.70GHz, 1MB Cache, 1000MHz (2000 MT/s) FSB, Brisbane, Dual-Core, Retail, Socket AM2, Processor with Fan for 80.99 USD