You can find a good printing resolution tutorial by Ben Long at creativepro.com. From the intro: While Facebook, Flickr, email, and other online sources are great ways to show and share photos, at some point you'll probably want to make a print of an image. (For one thing, an archival print is still the most durable way to preserve photos.) Whether you print it yourself using a desktop photo printer, or send your images to an online service, you're going to have to size your image and choose a resolution.