I've been trying my hand at this HDR lark. What is HDR I hear you cry? if you don't know, I'll try and give you a brief understanding thus....HDR is short for High Dynamic Range. The human eye is a remarkable piece of kit capable of discerning a wide range of tones in a given light situation. When you're out and about in the daytime and the sun is shining if you look up at a building, you'll pretty much be able to see quite clearly, the detail of the building. Despite it being bright and contrasty, your eyes can handle it.
Point a camera at the same scene though and you'll notice that when you look at the resultant image, there's a good chance the building will be in shadow and the sky behind it will be correctly exposed. Your camera's 'dynamic range' is nowhere near as capable as your eye.
HDR then, is a method of post-processing either one image or a series of images, (correctly exposed, underexposed and overexposed) and combining them and adjusting the contrast ratios to do things that are virtually impossible with a single aperture and shutter speed.
HDR can be done with single image (preferably from a RAW file) but it is always better to get at least three images as described above and combine them.
There are oodles of articles and books on the subject of HDR and I urge you to read them and practice.
HDR can bring a lot of life into your old images and using the relevant software it gives you the back the creative urge. You can get all kinds of goofy stuff, over-saturated colours, huge amounts of grain etc or you can strive to capture a more 'realistic' image more akin to the way the eye would see it.
I'll post a quick 'how-to' next time