Evening disband, this should work for you.
<?php
// The usual key/token/secret stuff that is required
$consumerKey = '';
$consumerSecret = '';
$OAuthToken = '';
$OAuthSecret = '';
require_once('./twitteroauth.php');
$tweet = new TwitterOAuth($consumerKey, $consumerSecret, $OAuthToken, $OAuthSecret);
// Here we are GETting just ONE status from my account
$foo = $tweet->get('statuses/user_timeline', array('screen_name' => '@dalehay', 'count' => 1));
// And now $tweetid is the variable that'll show your latest tweet ID
$tweetid = $foo[0]->id;
// Here's an example of how it can be used
echo "My most recent tweet's ID number is " . $tweetid;
?>
I used that (hence the random hello tweet to you) and it comes back with:
My most recent tweet's ID number is 677555879307251712
Hope that helps. 