Size 480 x 360
Go to the Media application on your BlackBerry handset. Pick the Pictures icon, and click on it.
You will see folders listed that have pictures in them. Open up one of these, and highlight to picrue you want to use for your wallpaper.
Then click the menu button. You will be presented with several options including Set As Home Screen Image. Click on that. The picture you have selected will now show up as your wallpape