with tbb, you dont spawn threads, you spawn tasks. These tasks are then typically divided up between the exisitng hardware threads to be processed. In this way, you do not code for a 4 core platform with tbb, you code for a multi core platform, regardless of whether there are 64 physical cores or 2 --the code is the same.
So, what is it that you want to do with this program? If you intentions were to create as many threads as you have in cores, then somehow assign those threads work to do, then that isnt really what tbb is designed for.
I suggest going over the getting started, tutorial and the reference manual to see how tbb works.