single post show message according to category tht post is in

This would need to be in The Loop in your template:

<?php
$message='';
if (in_category('2') ) {
$message='hello dude';
} elseif ( in_category('3') ) {
$message='proper bo';
} else {
$message = 'nothing to say';
}
echo $message;
?>

ah sorry i should have said its to run outside of the loop, can i run a separate loop to deal with this?

Don’t be confused by The Loop. Even single post templates (e.g. single.php) have a loop–even to display just one post.

Exactly what I needed!
thanks ??