There is an easy way to create a custom page for a particular page using Wordpress that doesn't involve adding custom page ID checking code. This might be useful if you want to remove certain aspects of the theme (like a side menu) just for that page. The way this is done is by using the Template Name tag in the following manner.
<?php /** * Template Name: Page Template */ ?>
Make a copy of your default page template in your theme directory and put this snippet of code at the top. You will now find that when you open the page to edit it there is a section called Page Template. This contains a drop down list of all of the templates available, including the default. You can create multiple page templates by just changing the value of the Template Name tag.