I am happy to report that plotalot works like a charm. Very easy to install and start to use. I had my first professional looking charts on my site in just minutes. The manual explains most of the tricks needed to get the charts you want. Since the data displayed is taken from SQL queries one have to learn/google SQL.
Support from the author was very good when I found out my download time had expired while I was waiting for the 1.6 version.