You might need to ask your host how to set that to run every 10 minutes etc
*/10 * * * * /usr/bin/wget --spider http://www.viperalley.com/classifieds/sendnotice.php
Thats the example cron Michael posts so that tells me you place * everywhere except hour which you would place /10 maybe and then on the command line you enter
/usr/bin/wget --spider http://www.yoursite.com/classifieds/sendnotice.php
Your host would know more on their regulations concerning crons through. Our examples are all for the command line crons the graphical ones like yours they work the same you just need to place the right info from that command line down the line on the right lines.