i've done it before, .. you have to make your script something like this:
Code:
#!/path/to/php
<?
echo "my php script";
?>
[SHELL]# chmod u+x script.php[/SHELL]
edit cron "crontab -e"
[SHELL]* */2 * * * /path/to/script.php[/SHELL]
disclaimer: this is all just theory .. haven't done it in a while =)