Digital SLR camera not focusing correctly?

I have a Canon 300D Rebel digital slr camera that does not focus (auto-focus mostly) and I am not sure if this would be a lens problem or a camera problem. It happens if i attempt to focus on objects within a few metres away so there really shouldn't be any problems. I tend to get more out of focus pics than i do focused pics. Would appreciate advice before I send to manufaturer for diagnosis. Thank you.

thank you for all advice, in reply to Jonathon the hunting is continual and drives me nuts.

I would check to make sure the subject is further than the minimum focus distance of the lens. Then I would also check your shutter speed as well. The speed of the shutter should be the recipocal of the focal length you are shooting, but dont forget to add your crop factor of the sensor. So it would look something like this 200mm lens x 1.3 crop factor = 260 which you should have your shutter speed equal to or faster. If that does not fix your focus issues, check with your local camera shop and see if they could have it sent to Canon service center shouldnt cost anything if under warrenty.

Some cameras require a two step process when pressing the shutter. As you initially press down, it activates the auto-focus. then, going further, it takes the picture. Unfortunately, this means a delay and the moment may be lost or the object gone from the viewfinder. Not that familiar with this model but some digital cameras also have settings for portrait or landscape. this sets up the focus to a limited range. You may also be able to select your aperture setting for greater depth of field. You then live with the shutter speed the camera selects based on the available light. Keep playing with the camera for a while on unimportant subjects around the house to become more familiar with your options. (When in doubt, read the manual). They are digital pictures and can simply be deleted. Then you will become more prepared for the pictures that are important to you. Canon makes good cameras.

Assuming you're not doing anything incorrectly with your camera, I would say it's the focus sensor in the camera body. Try using different lenses, and then try using different focus points. That may confirm the source of the problem.
Also, is there hunting, or does the lens go straight to the wrong focal point?

One strategy to try is to change the location of your subject in the viewfinder. Does that change auto focus? I use this same idea (focusing on bright spot in the viewfinder, keeping my finger halfway down on the button and then changing the composition and then snap the photo)when I want to over or under expose a shot, but want to keep my SLR on auto. You can also repeatedly hit the button half-way to change the depth of field. The camera will try several focal lengths and you need to tell it which one is correct. Trust your eyes.

Sometimes I think manual focus is almost faster than auto.

Is the subject within minimal focusing distance of your lens?