How to make an archive page template using WordPress 3

Archives.php is usually not a page template – it is a file used to display all the archived posts (usually some sort of list …)
It is usually triggered by a function that deals with archived posts like

<?php wp_get_archives('type=monthly'); ?>

Anyhow –

A page template file has to have this code in the begining ;

<?php
/*
Template Name: put name here  
*/
?>

in order to show as page template ..

so should you really want to make archives.php to work as a template file –

/*
Template Name: Archives
*/

should work.