How to Install Solr 3 on Drupal 7
Download the Apache Solr 7.x-1.x-dev module from the Apachesolr module and place it in your drupal folder for contributed modules. Typically this is sites/all/contrib
Enable ApacheSolr and ApacheSolr Search modules in admin/build/modules
Download Apache Solr http://apache.megamobile.be//lucene/solr/3.4.0/apache-solr-3.4.0.zip
Unpack it somewhere outside your drupal installation and outside your web root/folder. Suggestion would be ~/Servers/apache-solr-3.4
Go to sites/all/contrib/apachesolr/solr-conf and copy all files to ~/Servers/apache-solr-3.4/example/solr/conf
In ~/Servers/apache-solr-3.4/example/solr/conf you can remove schema.xml and rename schema-solr3x.xml to schema.xml
Open your command prompt and do cd ~/Servers/apache-solr-3.4/example
Type the following command to start the Apache Solr service
java -jar start.jar.
If all went well your Solr Server is running now! Congratulations!
Test your solr server admin interface by visiting http://localhost:8983/solr/admin
Go to admin/config/search/apachesolr/settings and click on edit. Verify if the url http://localhost:8983/solr/ is correctly entered and click ok
Optional(Facets): If you want Facets you should download Facet API and enable it. When this is done you can go to admin/config/search/apachesolr/facets and enable the facets you'd want
Optional(Security): Careful because Solr comes unprotected. If you'd like to run Solr in a more permanent basis I would recommend to run it on Tomcat as described in my other guide http://www.nickveenhof.be/blog/setting-drupal-6-apache-solr-tomcat-6-and... and put an IP-filter in front of it.
Optional(Multicore): if you want to run multicore you can type java -Dsolr.solr.home=multicore -jar start.jar.
Attention: All your files should be in multicore/core0/conf