Why am I doing this? Because my development server is also PHP 5. I also wanted to try all of the features of CiviMail, which requires PHP 5. In truth, this host doesn't have the mail software that CiviMail needs, so I don't really need to stick with PHP 5.
I installed a second, fresh version of Drupal and CiviCRM, this time using PHP 4. I discovered that the culprit appears to be CiviCRM, because if I disable it, I do not this error.
I will ask the CiviCRM list if anyone is aware of this issue.
Thanks, Hershel