Thank you for all your help so far :)
I have tweaked it to best suit my site and almost have it working exactly how I want it to.
Functionality wise it is perfect, I just need to tweak aesthetics now!
I have slightly edited the code you gave me, this is what I am using.
echo $preview; // echo the preview image
previous_post_link('<h6 style="float:right;">%link</h6>', 'Next project', TRUE); ?>
<?php next_post_link('<h6 style="float:left;">%link</h6>', 'Previous project', TRUE); ?>
If you take a look at one of the portfolio posts, such as: http://www.benrobins.com/dirt-3-game-trailer/ you can see the 'Previous & Next' links at the bottom aligned to the right and left. The only thing is, they are not on the same line! If this could be resolved so that they are both on the same line whilst remaining aligned right and left as there are now that would be perfect!
The other small issue is I would like these two links to always appear with a line above them to separate them somewhat from the post. To achieve this currently I have to add a ul /ul to the bottom of the post. If this could be achieved automatically that would be brilliant.
Many Thanks, Nearly there :)