Use the Magic Wand tool to select the white area. Make sure you have the proper object selected in the Object Manager.
Click "Selection Options" and make the selection area tranparent.
You will have to do this for each object, UNLESS... If the area to be made transparent is exactly the same in all objects, then CTRL + click or SHIFT + click to select all the objects, then "Make selection area transparent."
When you optimize the animation on the Optimization panel of the Workspace, make sure the Transparency button

is on.
Also, you may find plenty of information here:
http://vikingswebanimation.ca/tuts/uga5basicsf.htm