I do not have any experience with the Perl interface, but do use pvm, specifically
pvmgmake. It cut our build times down by 500%.
One of its aims is to be hetrogenous, so yes it runs on the major OS's (including windows).
Your question about the main executable is a good one. I have no idea. One would think so...
I agree that it looks like you need to design your application with pvm in mind, but this looks to be unavoidable. I cannot conceive of a general way to add parallelism after the fact: how the spawned processes synchronisation be completely general?
I would be surprised if pvm is not still active (their website is still updated):
http://www.csm.ornl.gov/pvm/pvm_home.html
http://www.netlib.org/pvm3/
Not sure about the Perl interface.
--
bm