To create a customised homepage copy your index.php file and call it home.php.  WordPress will use home.php for the home page of your site if it finds one, otherwise it will use index.php (there is also a more complicated way by changing settings).

Showing posts from a specific category on the homepage

Add this before the loop

<?php query_posts('cat=2&showposts='.get_option('posts_per_page')); /*SPECIAL - ADDED TO ONLY SHOW POSTS FROM 1 CATEGORY ON HOMEPAGE*/ ?>