Did you press F1 from inside prontoedit and read about transparency?

Did you read this thread as well?

[Link: remotecentral.com]

FYI, to eliminate the white, you will need to use selections and masks. Not necessarily easy to do but is possible in the software. To make partially transparent, you will need to put a transparent layer underneath (not white) and then put the current image layer on top. Then, for the image layer, set the layer opacity from the layer palette (F8) to something less than 100%.