Custom Query to Show Specific Post

Hey, strange problem that I’m having trouble searching for..

I’d like to show a single post on the home page. It should be:

1. The most recent post from the children of a parent category.. and:
2. Exclude posts from certain predefined categories.

The code I have so far is:

global $post;
$args = array( 'numberposts' => 1, 'category' => 174 );
$myposts = get_posts( $args );
foreach( $myposts as $post ) :	setup_postdata($post); ?>

I’m having trouble excluding the two categories I want to be ignored.. any help greatly appreciated!

Thanks,

Toby