Adding Non-Blog-Related Pages

First of all, I’m sorry if this has been answered in the past. I don’t have a lot of free time, so I spent as much as I have to search for an answer to this, but didn’t find anything.

Onto my problem: I want to have pages on my site that have nothing to do with the blog; such as a portfolio page, an image gallery page, etc. However, I want the blog and the other pages to be like one site, so the non-related pages should still be in the navigation menu and use the same templates. How do I go about doing this?

For example, I tried to make a page (using Write Page) with a PHP script on it (an image archive), but it came out as plain text, not code. As an alternative, I tried to open the index.php page and edit it by hand; took out the blog posts and put in the image script instead. That gave me a load of PHP errors that just would not go away.

I really appreciate any help. Thank you for your time.