Pretty Much the Same Thing......
Some of the naming conventions have changed, particularly with Intel. This is being done to simply distinguish one line of CPU from the another.
Earlier Intel Dual Core offerings were called "Pentium "D" in the trade. The performance of these CPUs is nowhere near the newer line called "Core 2 Duo". Since the P4 line of single and dual core CPUs reputations were tarnished by running hot and not having the performance of AMD's similar offerings, Intel retired the "Pentium" brand for a while, but reactivated it with the new Pentium "Dual Core" E2xxx series. These are fine performing lower priced offerings, they just don't have as much L2 cache as the C2D series.
The issue of whether there is one or two separate processors on the actual die is sort of moot, the net result is pretty much the same. As you pointed out, Windows recognizes them as two separate CPUs. It's always fun to pull up "Task Manager" and see which of your programs utilize both of the cores, and to what extent.