You have a nice image editing program right? Good, now this is pretty easy, just keep the image sizes in mind, and your practicably done!
Startup and shutdown screens are actually bit maps saved in 256 indexed color. You create your graphic in a normal size and then follow these steps:
Step One: Convert your bit map to indexed 256 colors and save in bit map form. The safest form to save it in is "System" colors for those last holdouts using 256 color settings, but if you are using photos you will need to use an adaptive palette. If you use an adaptive palette, you have created a True or High Color theme.
Step Two: Resize it to 320x400 (don't constrain proportions... Windows stretches this back out to fit the screen). It will be totally skewed and weird looking. Make a backup copy of the image NOW!!
Step Three: Use this program to add an animated bar to the bottom of the screen. Just run the image through the program.
Step Four: I for one have found that all the images I've worked with at 256 colors turned out crappy at this stage. You're probably going to have to do some minor image manipulating. Bring the backed up file into your image editor and trim off the bottom 11 pixels. Cut/Copy the whole image into the clipboard, and paste it over the image you just applied the bar to. This will fix the picture's colors.
Step Five: Rename by the following conventions:
Startup Screen: Logo.sys
Shut Down (waiting): Logow.sys
Shut Down (complete): Logos.sys
There you're done! That wasn't too hard was it? :o) Windows will take the skewed bit maps and adapt them to the screen resolution the viewer is using. A good tip is to create your graphic LARGE. Either 800x600 or 1024x768. That way, when Windows stretches it out it will look good on everyone's screen.