The topic says it all, really!

I have a VPS (apache2) to which I have root access. I've installed Tomcat, and installed Solr, but in Drupal I get the error message

"warning: require_once(Zend/Json/Decoder.php) [function.require-once]: failed to open stream: No such file or directory in /var/www/vhosts/{sitedomain}/httpdocs/sites/all/modules/apachesolr/Drupal_Apache_Solr_Service.php on line 10."

I've tried following http://jamonation.com/node/856 and http://19thstreetdesign.com/blog/2009.02.04/instal..., but no-one seems to do a complete end-to-end set of installation instructions. It all seems horrendously complex.

I'm happy to start from scratch with solr (or to scrap solr all together), or fix the problem if there is a nice easy fix.. (this is a live server, although I can play on a test implementation, so starting everything again from Drupal upwards won't be possible)

Thanks in advance

Pete.