Well..... you're doing to have to be a little more specific on "dual core" as this has a lot of meanings
1.) Dual core cpu (which covers all cpu with 2 cores)
2. A particular dual core cpu. This would be
Intel: Pentium D, Celeron (dual core), Pentium Dual-core, Core 2 duo, Core i3, core i5 (6xx's)
AMD: Althon II x2, Althon 64 x2, Phenom II x2 (im sure there more from Amd but im to lazy to look it up.)
Although for seening this question before, im gona have to guess Pentium Dual core is what you're meaning and it is the faster of the 2.
Pentium D is based off the slow and hot Pentium 4 (acctually it really just 2 pentium 4's glued together) while most of the Pentium Dual core line is really core 2 duos with shrunken L2 cache. (newer pentium dual cores (G6xx i do belive the model # was) close to the core i3 with less l3 cache and no Hyper threading.