Currently all Core i3 processors have two cores.
All shipping Core i7 processors have four cores but they each run two threads at a time so in a sense it's 8. Your computer will even recognize it as 8 cores.
The Intel i7 has 3.06 GHz and 2.93 GHz core speeds Four processing threads 4 MB of Intel® Smart Cache Two channels of DDR3 1333 MHz memory
Dual means two, so two separate cores
As the name suggests... four. Two on each of two dies.