Sorry, but Intel AMT requires one of the Intel vPro processors (Intel Core i7 or Intel Core i5) that are listed here: http://communities.intel.com/docs/DOC-5583.
(The only subset of Intel AMT is the Intel Standard Manageability Feature set and I don't think that will work with Intel Core i3 processors and your chipset.)
I'm unsure how you are going about enabling AMT functions (I had to access the MEB-X menu with CTRL+P if I recall correctly during boot) - but I am successfully using AMT with an i3-2100 in a Dell OptiPlex 990. Unsure what the motherboard chipset is on this one - you are correct that full vPro and KVM is not available, but the other functions seem to be (Serial Over Lan, IDE-R, etc).
Hope this helps,