Editing index file in child theme

please advise how i get ONLY THE MOST RECENT blog posting FROM A SPECIFIC CATEGORY to appear on my index page (http://greenrefurbishing.com/wordpress/).

i’m building a child theme of Twenty Ten. Should I be editing the index.php file in the TwentyTen theme folder? Or the index.php file in my child theme folder, or something else? I’ve already made changes to the index.php in the child theme folder in order add in that slider that you see.

and after identifying which file, what code do i put there to get just the most recent post from a sepecific category?

FYI, i was just starting to slightly get my head around child themes and the loop before 3.0 but now i’m completely lost. please advise. thanks in advance!

nevermind. figured it out.

$latestposts = get_posts('numberposts=1&category=12');
foreach($latestposts as $post) :
<a href="<?php the_permalink(); ?>"><?php the_title(); ?></a>
<?php the_excerpt(); ?>
<?php endforeach; ?>