Displaying a different product template is very easy to do. But you need a "trigger" in order to know when to switch the template. In your case the trigger is the categoryid.
Thankfully the main category id for the current product page is stored in the $product array. So you can switch templates based on some code like this:
Code:
{if $product.categoryid eq '243'}
Do this
{else}
Do that
{/if}
A brief visual overview of how to determine what variable to use can be seen in this tutorial:
http://www.youtube.com/watch?v=lSb0dBP6I98