I use Irfan View to create WVGA wallpaper. I found that Irfan View allow you to customize your crop aspect ratio and dimension. Another good thing about Irfan View is its FREEware, to download click ‘Irfan View’.
You also can use Google Picasa to crop and resize photo but Picasa wouldn’t let you custom crop, you only can select a preset aspect ratio 16:9 and export an edited photo to resize it. This preset will not generate an exact resolution 480x800 instead its will converted to 450x800. Nothing wrong with this resolution, its still can fix nicely in your device it just that your device will stretch the photo to fill the missing pixel. You and your friend may not notice it's. This method still work and I will share both methods.