Need to combine registration forms...newbie needs help

Hello all.
Ok, here's the deal...web design, i can do. Coding this kinda thing, I cant. lol. What i need to do is this:

I need to alter the signup form so that where people input their preferred usernames and passwords, it will check them against another file, to make sure that they are already registered members of my site first. Then the registration will go on as usual, and the username and password registered for the board.

Is this possible? If yes...how do i go about doing it?

Cheers for the help

do you want it to check another "file" or another mysql database. The later is easy the former a little harden, i can;t do file checking yet so can't help you there, if it is mysql i could.

ok...umm...all i need to do is find some way of checking if a person trying to register on the board is already a members of the site itself. If they are, it will allow it. If not, it will prompt them to request membership. It needs to check both username and password, to make sure that no fraud occurrs

Why not just make a doorway page with a password and username input box, and when they pass they come to your secret forum wich you can change the url of on a monthly basis. I don`t think this is hard even though I can`t do it :-)

yes i understand that, but where is the information about them being a member of the site itself stored? text files or mysql?

also what do you mean a member of the site itself? is there a password protected section or something? if so why not just have the signup form there.

we need more information about how your system works before we can really help.