AMD Opteron 1218 vs Dual CPU E2200

They both are Dual Core. The E2200 is more energy efficient, but it doesn't support VT.

I'm going to assume you mean dual core E2200 since because it is not a server processor, it does not support multiple CPUs on the same motherboard.
I believe the opteron you mentioned is just a bit more powerful, especially with the extra meg of cache. If you want to be overclocking, I believe the pentium would do better since it is 45nm vs the opteron 90nm.

If you are purchasing them new, the opteron is definitely not worth the price premium unless you intend to put multiple CPUs on the same motherboard. This is basically the only reason for the price premium of the opterons vs the consumer desktop counterparts.