Thank you for your reply!
I use Notepad++ for coding now, and I like it very much.
And yes, we will be working on different files a lot, all the classes will be in *.class.php files, and so on.
But I was wondering if anyone have had any experience working this way?
How do you prefer to inject your code into his design? Should I teach him a little Smarty? or are there any other ways of doing this?