Frank White, I am sure you already know how to change your background , But I do want to start there:
To change your desktop background
1.Open Display in Control Panel.
2.On the Desktop tab, do one or more of the following:
Click a picture in the Background list. In Position, click Center, Tile, or Stretch.
Click Browse to search for a background picture in other folders or on other drives. You can use files with the following extensions: .bmp, .gif, .jpg, .dib, .png, .htm. In Position, click Center, Tile, or Stretch.
Select a color from Desktop color. The color fills the space not used by a picture.
To open Display, click Start, click Control Panel, click Appearance and Themes, and then click Display.
You can use a personal picture as a background. All of your personal pictures located in My Pictures are listed by name in the Background list.
You can save a picture from a Web site as a background. Right-click the picture and then click Set as Background. The picture is listed in the Background box as Internet Explorer Background.
If you choose an .htm document as your background picture, the Position options are unavailable. The .htm document is automatically stretched to fill your background.
Those instructions of course are for Microsoft http://www.microsoft.com/resources/docum...
Now the other few things that can happen with any malware ar virus attack is that your registry gets changed. Little tricky but I hope that this makes sense to you:
go to Start
got to Run
Find this registry key
and change the DWord value: 1 prevents changing wallpaper, 0 allows changes.
The other changes that malware can produce should be rectified by
1. Click the Windows "Start" button and click "Control Panel." In the opened window, click the "Appearance and Personalization" link. Click "Personalization" in the new screen and then click "Desktop Background."
2. Click "Browse" to open a dialog window where you set a custom picture. You can also use one of the Windows background images by selecting a pre-made background from the drop-down box.
3. Click "OK" to save your settings. The properties window closes and the background image is shown immediately on your desktop.
more info here http://www.ehow.com/how_6806170_enable-d...
This should enable you to access your Desktop images
http://www.howtogeek.com/howto/windows/c... shows you how to change your registry to start looking for desktop backgrounds in a different directory vs. the default directory. There you can also check if your Directory is set to the windows default. I believe by default windows xp looks at 3 default locations for images as backgrounds.
2. C:\WINDOWS (This is the folder that has the original backgrounds)
3. my pictures folder.
I hope this helps and let us know how it turns out. Good Luck