Different style / layout for each post?

I’m going to be using WordPress as a CMS for a video download site. I am new to PHP and CSS, though I’m more familiar with the latter.
Comments will be disabled on my site, users referred instead to a forum (like PHPbb). Each post will contain an image from the video with some supporting text, then a download button. More information on the video can be viewed by clicking on the title of the post to see the full entry.
Now here’s my question: For these “full entry” pages, is it possible to lay each out with a different look — one that would reflect the subject matter of the video? I like the way that WP handles post and organizes them, and know how to tweak the wp-layout.css, but with my current knowledge all I’d be able to do is give EVERY post the same look.
I’ve looked through the support forum and haven’t found an answer, though part of the problem may be the terminology I’m using. I did read something about calling another PHP file that is attached to a different .css, but I don’t know how to implement that, nor whether it’s the most efficient way to do what I want.
Any ideas?