I've been trying for the past week to get tomcat working with phidgets.
The problem is that tomcat uses a number of different classloaders to isolate each of the web applications.
You're supposed to be able to place the libraries in question in /share/lib, or /lib, but I'm either getting the error above, or the classloader can't find the phidgets jar.
I've tried running the phidgets via a web service, but it seems that the phidgets21.jar still tries to load the jni libraries, which fails.
I've admitted defeat I'm afraid. I'm going to run a standalone phidgets application, and then have the web application poll a shared database. A little inelegant, but it's more likely to work!