#!perl

use warnings;
use strict;
use Win32::OLE;

my $fs = Win32::OLE->CreateObject('Scripting.FileSystemObject');
my $d = $fs->GetDrive('g:');
print $d->{TotalSize}, " total\n";
print $d->{FreeSpace}, " free\n";
print $d->{AvailableSpace}, " available\n";
print $d->{TotalSize} - $d->{FreeSpace}, " used\n";
__END__
Output on my system, with G: mapped to a Samba share:
19447939072 total
16677601280 free
16677601280 available
2770337792 used