Adobe's website provides easy and often free downloads for their products, many of which are needed in today's web and business environment. See the link below for more information on downloads.
Photoshop Elements is Photoshop but with less features, so Photoshop is better but it is professional level software. For home use or to get started Photoshop Elements is OK.
Yes, for many reasons. But the main reason is Photoshop CS5's Content Aware feature. If you select a area in your photo and click the delete button on your keyboard it will fill in the background...