Hi Michael,
If you already have an accesible component that handles the Human Tasks, that's ok, there is no problem about integrating the engine with your component, but you need to be sure that you component is accessible via some APIs (java, ws, corba, whatever) and the component handles the lifecycle of those interactions (task-started, completed, suspended, etc). If your component do that, the only thing that you need to do is to create an implementation of the WorkItemHandler interface that will do the integration.
Cheers