Convert a String into an Array of Characters

You will want to use str_split().

$result = str_split('abcdef');

http://us2.php.net/manual/en/function.str-split.php

Don't know if you're aware of this already, but you may not need to do anything (depending on what you're trying to do).

$string = "abcdef";
echo $string[1];
//Outputs "b"

So you can access it like an array without any faffing if you just need something simple.