- create a folder
- copy the DTP (your screen size) you like in this folder
- open "Desktop Pictures" or "Appearance -> Desktop"
- drag the folder with the DTP on the "Picture"
- click "Set Desktop" and close the panel
- then you will get a different DTP at every "Restart"

please see this link to find a program for Mac OS 7.x users :

VersionTracker "Desktop Pictures"

If you use "AfterDark 3.x or 4.x" will work with OS 7.x, see "setup" then "WallZapper" and choose your picture.

- open the picture with GraphicConverter
- save as... "PICT in resource" named "StartupScreen"
- copy the file to the "System Folder"
- restart your computer and you will see the picture

Software see also:
TuCows Image Editors - TuCows Image Viewers

• Obtain Stuffit™ Expander for Windows (if you don't have it already), and install it following Aladdin's instructions.
  
• Download the package of pictures you want, making sure to obtain the appropriate monitor resolution.
  
• Unstuff the .sit, or .hqx file you downloaded with Stuffit™ Expand or Windows.
  
• Open Netscape Navigator™ (or your browser of choice) and view the .JPG images in your browser window.
  
• When you find an image you ant to use on your desktop, Right Click (in the browser window) on it and select Set As Wallpaper from the menu.

Software for convert to .bmp see:
TuCows Image Editor - TuCows Image Viewers

More Info & Tips:
Desktop Tools
Windows 95 Desktop Tips by BillsSite
Windows 95 Desktop Tips by OneStopWindows
The Complete Guide to Desktop Themes