Howdy Fred,
GPO and JBB are wonderful sound libraries, but it's like the difference between playing a whistle and a saxophone - there is more complexity to how they operate as well as the complexity of the sound you can get out of 'em!
There are some downloadable resources on
http://www.garritan.com/downloads.html that give the details about controllers for the instruments, and what they affect. I'm not sure what Garritan ships in their packages, but you might even want to check that page for updates to what came in your CD-ROM package as well.
There are also some tutorials on using GPO for orchestration, and getting convincing performances out of the instruments at
http://www.garritan.com/tips_tutorials.html. There are also some other interesting technique tutorials there. Check it out
ttfn,
Sherry