Public domain, open source, freeware, and free-use information can be useful in web design. Want a nifty font, graphic, or website layout? Chances are, you'll find one free somewhere online, and you're welcome to use it in your website, or distribute it as you see fit. Buyer beware, though: research carefully to be certain there are no use restrictions or copyrights on the item before you use it. Sometimes the authors kindly allow you to use an image however you like, but they want you to link back to them on your website. This has always rubbed me the wrong way - a "sneaky" (albeit legitimate, and anyway, you're the one who wants the graphic, aren't you?) way for people to plaster their names and "ads" on your website, whether or not their website is something you want to link to. If it's free, it ought to be free, no strings attached - but that's just my opinion. Otherwise, give some thought to making a Copyright page that explains who owns what that you used on your site, and always be sure you have documentation that you obtained permission to use it. (Keep copies in your files.)
Sometimes it's a case of "you get what you pay for." If it's free, is it of good quality? Is it on everybody else's website, too? You might want to learn Photoshop and make your own graphics, or create your own layout, or modify one so much that it bears no resemblance to the freeware template you pulled it from.
Always, always check into copyright if you have any doubt whether the item you're using is free. It's not worth a lawsuit, no matter how cool a graphic is.