Hey,
Your site doesn't really have to be "fit to screen". There are many times and many places where % are important, but in your case I'd leave the site as fixed. Site's like webforumz where using percentages that make the text boxes longer so people don't have to scroll so much is very nice. But a site like yours, it wouldn't really benefit your user much at all.

If you would like to learn how to do the percentage thing then I suggest going for it. But I don't think its something you must learn now for that site.

HTH