Is there a way to insert "0000-00-00 00:00:00" in a datetime database field?
In Drupal 7 DB API, support for the datetime type was removed. This means that you must use use mysql_type or pgsql_type if you want this functionality.  Below is an example of of to declare this schema provided your database is MySQL.  By setting not null to FALSE, you can store an empty value (''), which is equivelent to '0000-00-00 00:00:00':

'mydate_date' =&gt; array(
  'description' =&gt; t('My date field.'),
  'type' =&gt; 'varchar',
  'mysql_type' =&gt; 'datetime',
  'not null' =&gt; FALSE,
),


Note that to make the schema portable, you should provide a fallback type (varchar) for the case that the database is not mySQL.