Itunes automagically does it for you. You just drag the photos to the ipod (in itunes) works on both pc and mac
sorry I should have been more specific. I'm trying to put my personal pictures on the themebuilder app as a wallpaper. But, when I winscp them to themebuilder the pic is too big to use as a wallpaper. I need to resize them to 320x480 but I don't know how. Sorry for the confusion.