Pentium is an older intel brand name they started using a long time ago. They went through the pentium I, pentium II, pentium III, and pentium 4 before pentium was retired as their "high end" brand name.
It then began to be used in their low end core 2 based dual cores. The only difference between them and a core 2 duo, would be a lower cache.
Now intel has moved onto it's icore series, where the pentium is the name of their lowest end dual core part that lacks hyperthreading and turbo core.
That's all the info I can give without you being more specific with your question. Hope this helps.
Here's a link to intel CPU information from their first pentium models all the way to the modern core i7: http://ark.intel.com/