Cron problems after installing

Hi. I installed Acquia Drupal 1.2.19 (Drupal 6.14 core) on a shared server. These are the server parameters:
Apache version 2.2.13 (Unix)
PHP version 5.2.11
MySQL version 5.0.81-community

The install went just fine and I was able to set up a cron job. I set it up as:

30 * * * * /usr/bin/lynx -source http://www.*mydomain*.com/drupal/cron.php

My drupal install is in a subdirectory.

The job runs as scheduled by I get emailed a "500 Internal Server Error". I know this is usually a permissions problem. Is there somewhere I should be looking for the wrong permissions? Is there a definitive guide to the proper permissions on files and folders in a Drupal installation?

Thanks.