Things can be made transparent by using the "Transparency Max" slider in the "Surface Material" window (Render> Materials). Parts of an object can be excluded from the effects of "Transparency Max" by using a gray scale transparency map (TransMap). Light parts of a trans map will appear opaque, dark parts transparent. When applying a trans map, start by setting the "Transparency Max" slider to 100%, the other Transparency sliders to 0%.

Try using your graphic as both a texture map, annd a trans map.