Here is what saintmike meant when he said this is what "fork" is for:

...
# time to start a separate process, but we want the parent to keep run
+ning
# (i.e. parent and child run simultaneously)

my $childpid = fork();
if ( !defined( $childpid )) {
    die "couldn't fork: $!";
} 
elsif ( $childpid == 0 ) {  # this is what the child does:
    exec( "other_program", @args );
    # at this point, the other_program is running; it replaces
    # (has the same pid that was originally assigned to) the
    # "child copy" of the current script
}
# and here, the parent continues what it was doing...
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But as you have seen, it also works to simply include the ampersand at the end of the command line passed to "system()".