I tried looking for documentation but it is quite sparse. I wrote the following guide hoping that it might save someone 2-3 hours dealing with installations, setup and configura
Install & Configure Tomcat:
Add the following roles and user to the configuration.
Restart the server: /etc/init.d/tomcat6 restart
If all goes well, goto http://hostname:8080
Install Solr:
Install & Configure
vi /etc/tomcat6/Catalina/localhost/solr.xml
You should see Solr access on your Tomcat admin/manager page (http://hostname:8080/manager/html)
Configure Magento to use Solr:
Replace the original Solr conf directory with the Magento conf files. The trick is just to copy the directory from Magento, and replace the one in Solr. That's it!
Troubleshooting:
Make sure all configuration files belong to tomcat6:tomcat6
chown -r tomcat6.tomcat6 ...