It's possible, but it would have to be a dual-CPU board. You'd have 4 memory slots = 2 channels per CPU.
I don't know if an actual AM2/DDR2 equivalent exists, but here's one with socket C32/DDR3 (ASUS KCMA-D8)
http://www.newegg.com/Product/Product.aspx?It … N82E16813131670
(edit) I can't find any actual dual AM2 motherboards; you may have to look for socket F or socket L motherboards instead (the server equivalent of AM2), those were made with up to 4 CPU sockets and 16 memory slots.
I/O, I/O,
It's off to disk I go,
With a bit and a byte
And a read and a write,
I/O, I/O