What operating system are you using? Most modern operating systems (Unix, Linux, WinNT/2000 etc.) will automatically assign your threads to run on whatever processor is free at any given time. If you have a 2-threaded application, it will automatically take advantage of the 2 CPUs. There is no need to specify which processor the
thread will run on.
In fact, the operating system performs "time slicing" which implies your thread may be executing on either processor, and may in fact switch between processors!
Geoffrey