Photoshop is around £400 for CS4 its a fairly difficult programme to use, personally all though i have CS3 i dont use it i use adobe elements 6 retails for around £56.00

has elements of photoshop in it, its missing curves and a layers mask but this can all be downloaded for free and added on

basically the 2 soft wears do the same thing which is enhance your picture its a digital dark room, allows you to adjust hue,saturation,levels, brightness,
it also comes with lots of filters allowing you to get creative

you can design greeting cards and scrap book pages

personally from my choice i always use Elements 6 its faster and less complicated and once you know the inner workings of it , it can be scripted to add actions and filters