How to call a search block
What are you doing in your module?, If you are building a new entity, you would to use hook_apachesolr_field_mappings() http://drupalcontrib.org/api/drupal/contributions!apachesolr!apachesolr.api.php/function/hook_apachesolr_field_mappings/7

An example is the implementation in http://drupal.org/project/apachesolr_commerce 

Regards!