Hi Shawn - I did exactly what you are talking about using theWebAssist Registration Pack. If you have PHP installed correctly on your ASP server and you have access to the database server (on my test site, I used LINUX and MySQL but the process is the same), you should have no problem setting authenication up. If you do not have PHP installed or do not know then you would have to do this in ASP. The quickest way to find out (I assume that you have, at least, FTP access to your server is to create a test PHP page.
Open DW and select PHP page - open the page in codeview and add the following to the top of your PHP page - nothing else, like headers is required -----
name the page phpinfo and upload to your server
Now open a browser and go to your server's IP address/phpinfo.php - if the page displays, it will display the PHP installation info and if it does not, then you don't have PHP installed, when means that you would have to do your project in ASP. Not knowing which version of server software installed, I can't tell you much but you can use CMS systems like DotNetNuke to do exactly what you are talking about with little programming knowledge. If you have further questions, send me a PM