If you are looking to exlude feedapi nodes or webform nodes or maybe even node-types you ve created yourself using cck from your search results because they are not relevant.

Use http://drupal.org/project/search_block [4]

Install and go to the settings page(settings > search > tab)
You ll be able to restrict nodes on a content type base from your search.

If your site was allready indexed you should re-index it. Go to settings > search to do it. Run your cron until everything is indexed.