A Thirsty Mind
"Not sure I'm getting the entire gist of this thread but I think the question was why Kindle Previewer was cutting off the cover at the top and bottom of the screen, not displaying properly? If you choose landscape instead of portrait icon on the bar in Kindle Previewer, then everything looks OK to me."
Unfortunately I did not find that was the answer. You need to look at your cover carefully. When you change it to landscape, I think you will find another part of it (the bottom) has now been cut.
Also doughayman suggests it is only a problem with Win XP. No, I have used Win 7 all along. I am convinced the problem is in the (downloaded) Kindle Previewer.