Ehm, you ask in your subject a different question than in your post itself. First, the question in your title. The way to create new processes in Unix is fork. Nothing else. On which processor that new process is going to be run (and when) is the task of the scheduler, and not Perl. Different OSses have different schedulers.

As for your other question, there's not much I can say. At first glance, I'd expect the problem to be with the srub.pt.p process, or how you call it. Why aren't you checking $?, or the return value of system? What happens if you let both children execute srub.ast.p? Could it be that @ARGV contains characters that are special for the shell? (Perhaps you should use the list form of system).

Abigail