Once you apply for the second H1B and get approved your first (postdoc) H1B can be dismissed. So you will hold only one H1B at a time, not big deal.
But one thing to be careful, if the permanent job is not for university or non-profit organization, it will take quote, thus has to start from 10/1/07, then you need to maintain your first H1B status until then. You should consider the timing issue carefully. Talk to the second employer aobut this when applying the second H1B.