hypersonic is on if it is configured in the jboss config. It's great that you modified the files, but if you do not post what their content is, we can NEVER see what might be wrong.
Also , how did you deploy jBPM, is the hibernate.cfg you think you use actually used? etc..etc...etc.. there are lots of things you can and should try yourself which we cannot do for you. So please post more info
Thx for answering;
I just found : http://www.jboss.com/index.html?module=bb&op=viewtopic&t=86232
Going to invest that way
I give myself till tommorrow to find how to make it works; else I'll probably post one more time here ^^