user's rights ???

[Xpression]

        Hi list, I have configured a server to act as a WWW server, but I
have many users that have their own web page and they can access to their
sub-dirs via FTP, now when they want to upload the files via HTTP (usin PHP)
the system denied the write, I mean:

/usr/local/www/wwwroot/webmaster                      <- main dir
                                                        /user1            <-
user1
                                                        /user2            <-
user2

Everyone wants to uploads files via HTTP but I guess they have to
authenticate to write on their sub-dirs, any clues ??? Thanks...