ESSG 4.1.2 with all updates should work fine on a dual-processor machine, as long as the installer recognizes that that motherboard is dual-processor; SME Server v5 will work on dual-processor machines right out of the box (with the same caveat).
If the 4.1.2 installer is not recognizing your machine as SMP-capable, try SME Server v5; if that still doesn't recognize it, please let us know at bugs@e-smith.com.
(If we don't know about the problem, we can't fix it!)
Cheers,
-Rich