Site performance help

Some months back we migrated our site to Joomla but have since found the performance of our site to be unacceptable. Our site relies extensively on article content and Joomla appears to reach into the database everytime a page request is made, even though caching is turned on and despite the fact that we've installed a caching module. Performance is so bad now that the site doesn't load at all if more than a few people are visitng the site at one time. During our last flame out the server admin had this comment: "The load is due to your mysql queries. Mysql is trying to use 4 times the amount of CPU your package has allocated. When this happens mysql has to wait until more CPU is available to finish it's query. I would hire someone to recode the application/queries." Bottom line? We need someone to fix the Joomla / database connections so that the pages load fast. If you think you have a solution give me some idea of how you might attack this problem. Here is the address of the site: [login to view URL]