HDR is a process of making 3-12 bracketed exposures, (3-12 photos from over to under exposed to get a full tonal range.) mid tones, highlights, and shadows all in one photograph. You need to bracket each shot by 1/3, 1/3, or full f-stop, It is best to bracket using shutter speeds not f-stops. Shutter speed bracketing from 350, to 250, 90 is just an example. But changing the f-stop is not recommended in some situations.
The idea of HDR has been around for a damn near long time. The soft wear to do so, not so long. But HDR has been thought of for the longest time. Because traditionally you can not get a photograph to represent what your eyes seen. The highlights, shadows, and mid tones all in one. But as technology progresses so do the programs that are capable of producing HDR images. Photoshop CS2, CS3, and CS4 have merge to HDR options. But there are a few dedicated programs such as Photomatix that can do more features such as tone mapping, which gives the painterly, illustrated qualities that alot of people are producing.
Check out wikipedia.com for more info on HDR. It is so hard to fully get the grasp on a forum.
With out showing us the examples youre refering to, (lighting in the landscape) we can not fully understand what you mean by how they are lit. But post-processing is refering to a photograph that has been shot, adjusted, toned, edited in photoshop. Processing just means edited or altered to your style or desires.