I found a great deal of information on Pivot Tables on Datapig Technologies. It is a website I found when I was doing searches for Excel info a few years back. I ended up having my company at the time get a membership to the site. You may want to check it out.
A chap called Allen Wyatt, who runs a web site called "Excel Tips", put together a most useful booklet on Pivot Tables, and sold it as a PDF download. This was back in 2004. I think that he still sells it, and has put out a companion product for Excel 2007. Take a look at