Create a text file named desktop.ini. in the folder where you need to change the background. You may find a hidden file in that folder too with the name desktop.ini. If present open that file and add the following code at the end
[{BE098140-A513-11D0-A3A4-00C04FD706EC}]
IconArea_Image=complete path to the image file
Hi Guest we just wanted to alert you to a major change in the forum. We will no longer be allowing the posting of outgoing links. Please use the attachment feature to attach media to your posts.