Help With Thumbnail Resizing

Hey guys, I’m in need of some help for a new magazine site I’m developing.

I’m developing a different layout for a page dedicated to music/videos.

I’m using this code to pull the thumbnail from a post.

<a href="<?php echo $link; ?>" >
         <?php echo get_the_post_thumbnail($post->ID, array(300,200));
         echo '</a>'; ?>

I want to change that size to say, 150x100px – if I did do that the width would be 150 but the height will get inherited for some reason and it won’t be static throughout all images. How come? If there is a problem doing it this way, how can I overcome what I need by maybe having it clip the image instead of stretching or resizing?