Board Integration

I have been searching around for a while and going to forum to forum with this question. I know it's a little complex, but here goes.

Here is the run down of what I'm trying to do. I found a user registration script(PHP) for users to register and gain access to my site and it's contents. I have got that figured out pretty well. Now here comes the tricky part. I want to make the webpage so that users can post messages in a forum (for instance ICONBOARD) using there username without having to register a new account name for the forum. In other words, make it so that they can post messages using their same username without having to register all over again for the forum.

I have looked int PHPnuke, but i've heard a bunch of security issues that I don't feel like dealing with.

If anyone has any other ways of doing this, even if it takes using asp, i'm open.

~tekfile