Just a thought about something you might try... This works for me under unix, and I expect it would work in windows as well. It's very good in terms of using minimal memory, and having fairly low system overhead overall:

chdir $toppath or die "can't cd to $toppath: $!";

open( FIND, "find . -type d |" ) or die "can't run find: $!";

while ( my $d = <FIND> ) {
    chomp $d;
    unless ( opendir( D, $d )) {
        warn "$toppath/$d: open failed: $!\n";
        next;
    }
    while ( my $f = readdir( D )) {
        next if ( -d "$d/$f" ); # outer while loop will handle all dir
+s
        # do what needs to be done with data files
    }
    # anything else we need to do while in this directory
}
close FIND;
[download]

This has the nice property that all the tricky recursion stuff is handled by "find", while all the logic-instensive, file-based stuff is handled pretty easily by perl, working with just the data files in a single directory at any one time.