How to Set Backgrounds on a Jailbroken iPod
- 1). Open the Cydia application from your jailbroken iPhone's touchscreen and open the "Sections" menu by tapping its icon at the bottom of the screen.
- 2). Scroll through the Sections menu by dragging the screen with your finger, and select the "System" menu by tapping its name in the list.
- 3). Scroll to the "W" section of the menu and tap on the entry for "Winterboard." Install this application by tapping the "Install" button, then the "Confirm" button. When installation is complete, tap the blue "Reboot Device" button and wait for the iPhone to reboot.
- 4). Open Winterboard by tapping the icon that will have appeared on your iPhone's touchscreen. Tap "User Wallpaper" in the Winterboard menu and select the image you want to use.
Source...