One way to fix the "unable to fork" problem is to copy the cmd.exe file into your PHP directory. This way you don't have to give the IUSR account read and execute permissions to the original cmd.exe file in the \Windows\System folder, which is not good practice as it opens up a security hole on the server.
However, I'm still trying to determine if there are any negative implications to copying cmd.exe to the PHP directory, so treat this advice with caution!