Sample Code (PERL)

use Win32::AdminMisc;
use Mail::Sendmail;
use strict;
my ($total, $free, %mail,
 $machine, $drive, $low,
 $to, $from, # Email addresses
 );
$machine = 'DBSQL01';
$drive = "c:/";
$low = 50000000; # 50MB
$to = 'notify@address.com';
$from = "$machine\@address.com";

my $VERSION = 0.1;

while (sleep 43200) { # Check every 12 hours
 ($total, $free) = Win32::AdminMisc::GetDriveSpace($drive);
 print "$free bytes remaining\n";

 if ($free < $low) {
  %mail = (To => $to,
       From => $from,
       Subject => "$machine low on disk space",
       Message => "$machine is low on disk space again.
          ($free bytes remaining.)"
     );
     sendmail(%mail) or die $Mail::Sendmail::error;
 }  # End if;
}  #  Wend

source: http://www.rcbowen.com/imho/perl/disklow