Well, PHP can create whatever kind of image you want. JPGraph, which you're using, definitely facilitates that process.
Obviously, if you only want a graph to display a single product, then you'd only pass that data to JPGraph.
If you can create a tabbed dialog box using HTML (and possibly javascript), then you can generate that same HTML/Javascript code using PHP. Many sites (amazon and msn, just to name a couple) use a "tabbed" homepage interface (amazon assigns each "store" a tab, and msn assigns "MSN Home" and "My MSN" separate tabs). This implies that you can use the same thing, too.
I suggest the following: Have a form that uses checkboxes to determine which products should be displayed in your graph. When the user submits that form, select the data for only those selected products and pass that data to JPGraph's graph-building functions.
By default, you can have all the checkboxes pre-selected and the graph generated to display the data for all products.
Take care,
Nik
http://www.bigaction.org/