I have a project in mind and was wondering what language I should use.

I need a web page to do a user creation thing (I can do this part in my sleep).
The end result is that this will create a regular /user on my linux box.

I'm thinking that the creation page may be able to call a cgi of some sort that will call 'adduser' and pass the username and password from the web page to 'adduser'...

.... I don't know. Is there anything out there like this already? Am I treading in dangerous waters with the idea?

As Bones might say, I'm a designer, not a programmer.

Well, one obvious question would be, what stops anyone who wants to from creating a user account on your box?

have a look at webmin, i think it has a module for that, not sure though.