On ones of my sites, I use the forum database as the member database, and it works perfectly.
Unless your existing member system on your site is very complex, I would also recommend using Web Wiz Forums to manage the members for a number of reasons. 1.) Web Wiz Forums is more secure than many other login/membership systems. 2.) Its usually easier to modify the rest of the site to use Web Wiz Forums membership management than the other way around.
In most cases you would be able to simply add code to the header of your pages (as an include) that checks if people are logged into WWF. I simply included WWF's common.asp which does that automatically, but you could streamline it by creating your own include that checks if people are logged in (i.e. your pages don't need everything in common.asp, so you could eliminate some overhead by creating an include with just what you need in it). You then use the ASP variables set by common.asp to determine if someone is logged in, who they are, and what permissions they should have... passing that information onto whatever scripts you are using on the rest of your website.
If you have code or scripts that are looking for a specific cookies or session variables, you can modify the login script in WWF to set those in addition to the standard WWF ones.
I also created login pages that automatically redirect you back to the page you were on (based on the login page that WWF uses).
Since WWF's code is well documented and commented, it is easy to mod(ify).
I haven't upgraded to 8.0 yet, but as soon as 8.0 stable is out, I will begin making those 8.0 mods.
