Hi Mohamed,
Which version of jBPM do you want to use?
If you choose to use jBPM5 you can only use BPMN at the moment and it will allow you to manage human tasks and have a very cool Drools integration.
If you are planning to use jBPM3 and BPEL.. you cannot use BPMN and you will need to use jPDL or BPEL, not sure if the BPEL language will allow you to do too much.
Cheers