change something

Ok, say I have a file on my server. Using a form, how would I insert data into it?

IE: I enter "cf" into the name form. Then when submitted, this file will write to a config file that says this:
$name=""
and insert cf into the ""'s.

Thanks!

http://www.php.net/file

http://uk2.php.net/manual/en/function.fopen.php
http://uk2.php.net/manual/en/function.fread.php
http://uk2.php.net/manual/en/function.fwrite.php
http://uk2.php.net/manual/en/function.flock.php
http://uk2.php.net/manual/en/function.fclose.php

Plenty examples in there