hmm...I tried the URL and the PHP site doesn't come up with any vaild results.
Anyways...a checksum is a way of calculating a unique value from a piece of data. That way if the data is transmitted somewhere else the checksum can be performed and compared with the original checksum value. If the values are different then you know the data has been garbled in transit or tampered with.
As for the solution - the best way would be to use the md5() function.
http://www.php.net/manual/en/function.md5.php
