In case it's of use, I wrote a couple of scripts years ago to run an external command on both Unix and Windows, killing it if it took more than a specified timeout, and reporting how long it took to run:

• Timing and timing out Unix commands (using fork, exec, kill, waitpid)
• Timing Windows commands (first attempt using Win32::Process)
• Re: Timing Windows commands (improved version using Win32::Job)

I enjoyed using Win32::Job much more that Win32::Process. BTW, I never use fork/exec emulation on Windows, too much general weirdness and confusion between threads and processes for my tastes.