# Old Skool calls
use Win32::API;
my $getwindir = new Win32::API(kernel32 => GetWindowsDirectoryA => [qw(P N)], "N")
  or die "Can't locate function: $!";
# ... or use 'PN' for the 3rd parameter, if Win32::API is recent enough (version?)
my $buffer = "\0" x 300;
my $length = $getwindir->Call($buffer, length $buffer);
print substr $buffer, 0, $length;

##</code><code>##

# New Skool calls ($Win32::API::VERSION >= 0.40)
use Win32::API;
my $getwindir = new Win32::API(kernel32 => 'LONG GetWindowsDirectoryA( LPSTR buffer, LONG maxlength )')
   or die "Can't locate function: $!";
# Do this, or bear the consequences:
delete $getwindir->{proto};
my $buffer = "\0" x 200;
my $length = $getwindir->Call($buffer, length $buffer);
print substr $buffer, 0, $length;