OK, in that case what you will be doing is storing their pages inside of their home directories.
their home pages will be static HTML files.
You will need to use the fopen function of PHP to open the file and store it to a variable.
then you dump the contents of the variable into a text area
then once they are done you just store the file again. You don't really need to use the database for anyting but the login. There are functions in PHP that enable you to browse through directories and return files,
I'd suggest however if you wanted it to be really cool (or what I though was cool when I did something like this) is to store filenames and paths in a database so you can make a nice treeview without having to worry about the propery controls, (if they are even available in PHP).
(if you don't get what I just said about the tree view check out here
It's a part of my final year project from Uni, there was a login function as well, but I too that off