This class in PHP can be used to get the status of any partion on Windows, Mac OS and Linux.
Makes use of disk_total_space and disk_free_space.

Source Code

All source code is online here.

How to use it

require_once('DiskStatus.class.php');

try {
  $diskStatus = new DiskStatus('c:');

  $freeSpace = $diskStatus->freeSpace();
  $totalSpace = $diskStatus->totalSpace();

} catch (Exception $e) {
  echo $e->getMessage();
}           
There is a more complex example on the source page, which creates the following output (HTML + CSS): Disk Status HTML output