The image they are refering to is your preview image. It has to be 1024x768 or larger.
Play your MPG or WMV in windows media player in full screen mode. While it is playing, hit the print screen key on your keyboard and it will save the image to your windows clipboard. Open up the paint program that came with windows. Click on the edit button and then click paste. You should then have a screenshot in paint of your mpg. Click on file, then click save as and name it preview.jpg and save it to your desktop. You now have your preview image. When submitting your dream on the 3rd line where it says preview image you will need to browse to the image you created.

-sigh-

We are talking about different things.

DreamMaker requiers a thumbnail.  Wincustomize requiers a Preview (which it converts to a thumbnail on the site)

So . . take a screenshot of yoru dream as described by carguy.  Save it as somethign big (1024x768 or larger).  Resize it with some imaging software to 256x256 (or smaller . . but why?).  Save it as a different name.

Use the small image in DreamMaker.
Use the large one when uploading.

Clearer?

Ohh, i finally understand thank you.