You may have to do some experimenting of your own on this one because I am not too sure of how to do this anymore.
I know that there are two basic methods. For one you go to MS Paint and set the image atributes to 400(h)x320(w). Then you create what ever image you want. You can cut and paste images CDs or the internet or whatever. The next step is to save the file you just made as logo.sys to either the root(c:) directory or the Windows direcory. This varries depending on the version of Windows 9x you have and weather or not you have installed MS Plus! A good way to make sure it works is to save the image to c root and windows. All I have left to say about editing the startup screen is that I don't know how to do it in Windows 98 S.E. (Second Edition). You see, Microsoft wants you to advertise thier company every time you boot up. They have even gone to court to make sure that when a retailer sells a computer he cannot completely change it. He could put a little logo in the corner or something but he couldn't do much. If a large company changed thier startup screens then Microsoft would sue them but they don't seem to care as much if small companies and single users change the screen, but they still don't want you to so they hid the files that you use to make the change.That is why my first method is often the easiest.
The second method is harder to do and doesn't always work. You need to find the file named logo.sys (it is a .sys extention but can be changed with MS Paint)wich is usually in the root directory or the windows directory.
If you run Windows 98 S.E. as I do you are S.O.L. for changing your startup screen. I can't even figure it out. If you ever get it then please e-mail me.
Ok. That was all pertaining to changing the startup screen. Now it gets easy. The shutdown screens are a snap to change. You just go into the Windows directory and find the files called logos.sys and logow.sys and change them however you want just as long as you leave the atributes alone.