forum issue

let's say i already have a php-scripted website done, with login and registration system. Then i want to make a forum board for my website but i dont wanna go thru the work of scripting it.

Could I use one (like Mybb or PHPBB) and have it built in my website?
I dont simply want an external link to this forum board, i want the "new thread" and "read thread" pages to be inside my pages. Plus I want my already-scripted login/reg. system to be the same as the one from the forum board. Is this all possible or am i gonna have to code my own forum?

If you link your forums to the same database your current user information, yes, this is possible. However, you might have to change the table name to reflect what phpBB (or whatever forums you are using) will be trying to pull user information from; you will also have to rename the columns appropriately and add any that may be missing (or you could simply let phpBB create the new table and cron all your data over). Your standard login page (and all other pages that require access to user data table) would also have to be altered so that it gets user data from your new table (or you could altar phpBB to get data from your old table, but this would probably be a lot harder).

Ultimately, all you have to do is get your php pages to all gather user information from a single table.