I have had good success with fork on Windows (perl release 5.6+). However, you can also use a piped open command which will not wait for the output. If the trailing character is a pipe symbol, "open" launches a new process with a read-only filehandle connected to it. For example:

open(NET, "netstat -i -n |") or die "can't fork: $!";
# You could go off and do other things here for a bit,
# and then come back to check on your results.
while (<NET>) { 
   # your code here...
}
close(NET) or die "can't close netstat: $!/$?";
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Please note that when you explictly close the piped filehandle, it will cause the parent process to wait for the child to finish (and I recommend closing it).