You need to add a transparent background to all of your items. An easy way to do it is to first make it a colour that ISN'T in the part. After that, there's a free site called iaza: Free Online Image Conversion - Simple & Easy Converter (Images, Graphics, Avatars, Anime ...)
you can go to. In the box all the way to the right there will be an option called "Transparent". After clicking that, just follow the instructions.