I'll point you to a camera review site that explains everything for the novice but also goes pretty in-depth with it's reviews
www.megapixel.net
a full screen image is only about 2 megapixel btw if you want it for anything other than hardcopy prints go for a lower megapixel count and get nicer optics (stay with the better brands nikon,olympus,fuji,canon, minolta. Kodak and hp from what I've seen when I've used them are pretty horrible as are the gateway cameras)