It would be useful if you wrote what difficulties are you experiencing (see also TellTheDetails).
Anyway (and though I've nearly no experience with custom class loaders), I noticed you don't call resolveClass() anywhere in your code. The defineClass() javadoc's mentions the class needs to be resolved (ie. linked) before use. May this be the problem?
Edit: I assume you know you'd obtain the instance of any class by calling the Class.newInstance() method; that you tried this and it failed.
Don't get me started about those stupid light bulbs.