How to create a nook wallpaper
Wallpapers should be created as a JPG, PNG or GIF image that is 600 pixels wide and 760 pixels tall. The height is 760 pixels to allow room for the status bar that appears in the top of the window.
The type of image determines what format you should use. I discourage the use of GIF images, but it is supported on this site because the nook supports it. If your wallpaper is a photograph, use the JPG format. If it's not a photograph, but is either drawn on a computer or a series of line-art or geometric shapes such as a comic, use the PNG format.
There are many graphics editing programs out there that will work rather nicely. Personally, I use The Gimp because it's free and I can use it in both Linux and Windows.
Once you've created your new amazing wallpaper and have logged into nook-look.com, just click the "Upload File" link on any page.
You will be asked to choose a category (please choose carefully,) a title and a description. Then browse to the image you have created and upload it. There is no need to zip up individual images.
How to create a nook screensaver
Screensavers should be created as a JPG, PNG or GIF image that is 600 pixels wide and 800 pixels tall. Screensavers are slightly larger than wallpapers because they don't have to allow space for the status bar in the top of the window. A screensaver typically consists of more than one image.
Once you have a series of related images you want to turn into a screensaver, place them all inside a single folder and then zip up that folder. You can either use Winzip, or your favoriate zip utility. If you are using Windows, you can right click on your desktop and pick "New - Compressed Folder". Give it a name such as "MyCoolScreensaver". Then, drag the folder that contains all of your images and drop it on this new compressed folder. That compressed folder, or "zip" file, is what you will upload to nook-look.com.
Screensavers created this way will pick the first image as it's default thumbnail in lists on the website, and will report how many images are stored in the file. When viewing the details for this file, the first four images will flip through as thumbnails in a kind of slideshow.
How to USE a nook screensaver
Screensavers are nothing but one or more images that are stored in a folder. The name of the folder becomes the name of the screensaver on the nook. For instance, if I want a screensaver called "Automobiles" I create a folder on my nook at "screensavers\Automobiles\" and place the images inside of it.
For screensavers properly packaged as zip files, they should already contain a folder and have all of the images inside of it. Just extract the zip file and drag the folder into the screensavers folder on your nook.
How to manage your E-Book collectionFor E-book management, I recommend Calibre.