>When I run a .prg which creates a class, I get no errors. I assume that the class has been created but, where is it? In memory? If I attempt to createobject("ClassName"), I get an error message stating that "Class definition ClassName is not found".

Simply running the PRG that contains the DEFINE CLASS doesn't create an instance of the class; in order to create an instance, the DEFINE must be findable in the procedures searched according to SET PROCEDURE and the VFP search criteria (or if it's a visual class stored in a VCX, the VCX must be in the SET CLASSLIB list); you create instances of the class in memory via CREATEOBJ(), NEWOBJECT(), or by using a container's AddObject() or NewObject() methods. Eric gives you a good example.