Oracle option not listed when installing

I'm having a similar issue that reported in #785380: Oracle not displayed as an available database type during installation. The difference being that I'm a) on Ubuntu rather than Windows and b) not getting the errors that user reported.

I'm using the May 03 version of the Oracle module and Drupal 7 alpha4.

On the databases page of the install routine, I get..

Database type *
MySQL
The type of database your Drupal data will be stored in. Your PHP configuration only supports the MySQL database type so it has been automatically selected.

Looking at phpinfo output, I'm seeing oci8 enabled and reporting as expected. I just get no option to select Oracle for my database.

I am using PHP 5.3, but the system requirements link (http://drupal.org/requirements) you referenced in the aforementioned post says 7.x supports PHP 5.3. Is the issue that the Oracle module doesn't support 5.3? I would have expected errors in that case, not no option.

The other thing I notice is that the last post reported that the INSTALL.oracle.txt had instructions for populating the $databases array manually. The one in the version I have just says

cd
/includes/database/
tar xzvf

Am I missing a trick? I'm new to using Oracle with PHP, so if you have suggestions of ways to verify the problem is inside Drupal rather than in the PHP configuration, that'd be a big help.