The first thing you'll need to do is make sure you have the ZZIPlib library installed. If you have WHM, goto the Apache Build page, and just build apache with the "Zip" checkbox checked. That simple.

<?php
$zip = zip_open("zip.zip");
if ($zip) {
  while ($zip_entry = zip_read($zip)) {
    $fp = fopen("zip/".zip_entry_name($zip_entry), "w");
    if (zip_entry_open($zip, $zip_entry, "r")) {
      $buf = zip_entry_read($zip_entry, zip_entry_filesize($zip_entry));
      fwrite($fp,"$buf");
      zip_entry_close($zip_entry);
      fclose($fp);
    }
  }
  zip_close($zip);
}
?>