suPHP issue w/ Wordpress in its own directory

While trying to install Wordpress in a directory of its own I get an internal server error if PHP is set to run as the Siteworx user (suPHP). If I switch PHP to Apache mode the install script runs. The install script runs either way as long as I'm installing into the web root instead of a directory. I haven't tried any other PHP scripts except to say Drupal installed clean as silk a couple weeks ago in suPHP mode.

Correction: also get 500 internal server error with WP installed in web root.

Suggestions appreciated.