I copied the info here in case that link stops working in the future.
***How To Change the Windows Startup Graphic***
Before your computer displays the Windows Desktop, you're treated to an animated (640 x 400) Microsoft Windows advertisement. This graphic is embedded in the Io.sys file in your root directory, and is easy to change. If you don't want the logo's to appear, you may open "Msdos.sys" (hidden file at C:\) in Notepad. Add or edit the line "Logo=0" under [Options].
Windows stores the splash screen in the file LOGO.SYS. Even though this file has the SYS file extension and is marked as a system file, it's actually a bitmap file created in Paint. This means that basically all you have to do to replace the Windows splash screen is create a new bitmap and save it as LOGO.SYS.
Before you begin, you should rename the existing LOGO.SYS file so you have a back-up copy of the original splash screen. Since LOGO.SYS is a system file, Windows Explorer and My Computer consider it a hidden file, even though the hidden file attribute isn't set. Therefore, neither of these hard disk navigation tools will display LOGO.SYS unless you change the View option.
You can locate the LOGO.SYS file easily with the Find utility. To quickly access the Find utility from Windows Explorer or My Computer, use the [Ctrl]F keyboard shortcut. Once the Find dialog box appears, type LOGO.SYS in the Named text box, select the C drive from the Look in dropdown list, and click the Find Now button. Once Find locates and displays LOGO.SYS, right-click the file, select the Rename command, and then give it a new filename. For example, you might rename it LOGO.OLD. Then, close the Find window. By saving the file under a different name, you can restore it by simply rename the LOGO.OLD.
Note: If you installed Windows Me over Windows 95 with Microsoft Plus!, there may be an additional file in your root directory, Logo.sys, which contains a slightly edited version of the original advertisement. In spite of its sys extension, it is a bmp file and can be edited by MS Paint.
Within Win 95/98, in the root of your C: (main) drive is a file called logo.sys, which is your startup screen. In your Windows directory are logos.sys and logow.sys, which are your Shutdown and 'Wait till Shutdown' screens. They might not be there, when included in some other file. Placing new files with these names will replace them anyway. You can just rename a bitmap to a .sys file.
Animated Logo: You can create your own animated Logo.sys file and replace Microsoft's sartup graphic with your own. You can animate the graphic, but you don't have to use animate the graphic.
The size: If you view an existing Logo.sys in MS Paint, you'll notice that it is sized 320 pixels wide by 400 pixels high. The Windows startup routines stretch it out to 640 x 400 when it's displayed. You can create a new graphic at 640 x 400 — or at 533 x 400 if you want to maintain the 4:3 ratio (width to height) that is the standard for video monitors — and then use MS Paint or Paint Shop Pro to shrink the graphic to 320 x 400.
Color: Your Logo.sys file must have a color depth of 256 colors (8 bit), and its file size must be 127K. If it is 320 pixelsx 400 pixels x 256 colors, it will be 127K in size. The Windows startup routine will reject a Logo.sys file that doesn't meet these criteria.
After you create your bitmap, save it as LOGO.SYS in the drive C folder and close Paint. The next time you start your system, you'll see your new startup splash screen.
Note: If you delete Logo.sys, the graphic embedded in Io.sys will be used instead. Getting rid of Logo.sys doesn't make the graphic go away. But if you set Logo=0 in your Msdos.sys file, no graphic will be displayed before the Windows Desktop appears. Your \Windows folder contains an additional graphics file named Logos.sys. This is the screen you see when you exit Windows. Just as with Logo.sys, you can edit this file or create a replacement for it.