[development] SOLR

Hi, I need a multi-site search system but I am new in Drupal search. Firstly I tried http://drupal.org/project/multisite_search however it didn't work well, some words wasn't indexed. So I began to planning on setting up SOLR in order to use http://drupal.org/project/apachesolr_multisitesearch. (Google option is not sutiable for us.) Then I notice that there is a module such as http://drupal.org/project/nutch. So I am confused. Is there anybody who could explain difference between these modeule (even pure SOLR search)? I am also open to any suggestion about search, any module, SOLR w/o Drupal modules, any other search options... Thank you all in advance...