There is a performance difference b/w the two, pentium-dual core processors are used for low-cost systems. Believe the Pentium dual-core has less cache 1mb vs 2mb and lower fsb 533mhz vs 667mhz. Also believe, batter life is lower, as it does not feature intel centrino technology.
Looking at laptops to use for class and meetings and such to supplement my desktop, and I notice that HP for instance offers both in some of theirs systems. The name on the processor was Txxxx so I know it's not one of the "old" Pentium D models, but other than that I'm clueless.