Judy, most images will default print to 4x6 right out of the camera. The best way to be sure is to crop them yourself to a 4x6 that way you are sure to get what you want.
Kim My Creations Canon 40D, Canon 28-135mm IS lens, Canon 300D, Canon 18-55mm lens, CS3
Yup - crop them yourself. Oh and did you know you can upload them to Walmart.com? (of course if you have dial-up that might not be the best option.) I usually try to upload everything before I go to do my weekly shopping and that way they are waiting for me when I'm done. (I do one hour because I like instant gratification )