fork() needs to be supported by the kernel. The Microsoft kernels do not support it. Perl 5.6.0 emulates something rather similar to fork(), though only for Perl scripts, by using threads (but, as I say above, this support is too new to be of much use).

There is a FAQ on the fork() emulation for Win32 Perl, though I didn't find it in the short time I spent looking for it. ):

        - tye (but my friends call me "Tye")

Updated to s/to/not/. Thanks, PodMaster.