Just forget BPEL, I think we should wait till 2.0 version of it's specification , as you know current version does not support human interaction .
and also it is important to note that BPEL usage is for webservice orchestration.
So my suggestion is to go with workflow  engines that implement WFMC standard  like :EnhydraShark OR none standards ones like : JBPM and openWFE .
if I were in your shoes , I would consider JBPM .