adjust the wp-login to be the homepage (password protected blog)

hello,

i want to make my blog password protected, that only logged in users will be able to see the blog.
once a user insert the address of the blog – the login page will be displayed if he is not logged in.

i think i need a script in php that check, in the index.php, if the user is logged in or not. i think this is how it is supposed to be, but i am not a php programmer, so if you have a better way of doing this so please tell me.

i would appreciate any help,

thx
haim