By default, the CCK date field was in the following format.

• CCK 2011-10-01T00:00:00

You can get the timestamp from the above the string by the the PHP the strtotime() function.

<?php
  $node = node_load($nid);
  $timestamp = strtotime($node->field_cck_date[0]['value']);
  print $timestamp;
?>

Done =)

Reference: Return Unix timestamp from CCK date field