Stardock’s Bootskin freeware is a good software to change your bootskins easily. You can download it from stardock’s website.
If you try to create your own bootskin, you will have some diffuculties about pallette. Your image could have some weird colors. If your try to change your image pallette it wont work, because the problem is not in your main image pallete, it is in your progress bar image pallette. I am using paint shop pro to edit my images.To solve this pallette problem,you must save your main image pallette and load it to the progress bar image pallette.
Here is a preview of the bootskin that i merged a "Stargate" image and a Calligrafic "Bismillah" image.