Quick PHP wordpress help required. PLEASE!!!

Hi,
Im looking for a way to check the category and display a thumbnail based on the category. (this will be on the main page).
The code i have so far just pulls in an image if no thumbnail is set. See below.

Can anyone suggest a way to help me change it to select an image based on categories.
e.g - If category has tumbnail, display it. Else If category is Sheep - Display sheep.jpg.

Thanks.

<?php
$thumb = get_post_meta($post->ID, 'Image', true);
if ($thumb == '')
{ ?>

<a href="<?php the_permalink() ?>">
<img src="http://www.mysite.com/images/standard.jpg" 
alt="<?php the_title(); ?>" class="left" width="150px" height="150px"/>
</a>


<?php } ?>

Code (markup):

 

how much categories are there?

 

if (in_category('2')){
//Display thumbnail for cat 2
}
else if(in_category('5')){
//Display thumbnail for cat 5
}

PHP:

and change cat numbers as required

 

Like wd_2k6 said, that should do it. However if you have more categories, you should simply try a different method, like maybe adding a new custom field thumb_type or something, so you won't have to get to a lot of ifs and elses.

Good luck