Threads, with which fork is emulated on Win32, have some problems in perl 5.6.1. I ran into the issue a little while ago, myself.

If you are able to upgrade to 5.8.0, I found it works much better in this regard. Though, since you apparently got it working using Win32::Process, it's not really necessary. :)

bbfu
Black flowers blossom
Fearless on my breath