Can someone please tell me the answer to this very simple question.

How can you add a 2d image to a scene which has an aplha applied to it, the idea obviously is that the black areas of the alpha are transparent.

Thanks.

Dell XPS M1730
Intel Core 2 Duo T9500 2.6Ghz
500GB (2x 250GB) RAID 1 Sata HDD
4GB RAM
Nvidia GeForce 9800M GTX SLI