for all who have windows 7 starter installed on their netbooks, and cannot change the wallpaper, here's a software that helps you customize your windows 7,
http://renaudgerson.fr/StarterBackgroundChanger/en/
this creates a customize button on the right click menu, so you can change your wallpaper, you can even choose a bunch of pictures, and set them to shuffle, i tried the software, it is 100% malware free, hope i helped!
PS: the installation is in french so if anyone needs help, feel free to ask.