how to crawl when Solr is search engine?

I have just begun using Solr. I see that we have to insert documents by posting XMLs to solr/update I would like to know how Solr is used as a search engine in enterprises. How do you do the crawling of your intranet and passing the information as XML to solr/update. Isn't this going to be slow?

post.jar is absent in Solr distribution

I am an absolute noob to solr and I am trying out the Solr tutorial present at http://lucene.apache.org/solr/tutorial.html In the tutorial, post.jar is mentioned but I don't find post.jar anywhere. I downloaded the solr tarball from