Although this won't relate to coding using DW (I've tried and decided the best way to learn is to just hand code the php), I've just been working on a similar project and have found the "Creating a Membership System" by phpfreak (in the tutorials section of this website) and another membership tutorial there, "PHP Membership System 2.0" by Bradley Beard to be helpful in understanding.
I set up my database similar to what was shown in the tutorial, and being totally new to pulling data from databases and sessions, etc., experienced some problems but have been working through them with help in the Newbie Forum (Help with login script by ksp: http://www.phpfreaks.com/forums/index.php?...ic=14856&st=0&)
On our site, visitors come in and sign up for services (sign up info inserted into database from registration form), then with their user name and password they can log into a special members' only page (their info is checked against the database).
Anyway, the tutorial helped me get started... I still have more to do, like lost password recovery, etc., so am heading back to the tutorial now in fact.
Hope this helps,
ksp