Google your et1331G-03W, get this page, http://www.emachines.com/products/products.html?prod=ET...
discover your cpu is an AMD Athlon™ II X2 dual-core processor 235e, go to amd site and read specs for said chip,
you have an AM3 socket,
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Motopsychojdn, just because a CPU is AM3 does not necessarily mean that the motherboard socket is AM3. I have an Athlon II 620, an AM3 chip, which is running in an AM2+ motherboard with no problems.
Unfortunately for the OP, I do not know what the socket is on the motherboard. If you open the case and find a model number on the motherboard (usually between PCI / PCIe slots, at least in my experience), this should help. Search for that board, and it will tell you.
Its probably an AM2+ then. While its possible for an AM2 to run an AM3 CPU, the odds of that being the case are pretty slim. If its running an AM3 CPU with DDR2 ram, its probably/most likely an AM2+ board.
A better question is why does he want to know? As an OEM/Emachine I doubt this info will help him much.