The intel pentium "Dual Core" Is it an Intel Core 2 Duo? And the pentium 4 is just a regular Pentium 4 3.8ghz with HT (Hyperthreading)?
My guess is your processor, being a dual core is probably the E2140 which is a Core 2 Duo processor. It's a newer and better technology then the Pentium 4. Despite the Pentium 4 being a higher mhz speed, I would stick with the dual core. You'll be able to use your computer a bit more broadly then with the regular pentium 4, since there are 2 cores working on processing the data, rather than the Pentium 4's single core hyperthreading solution.