Make sure the image(s) have an alpha channel and are saves as 32 bit WITH alpha.
Then the engine will render them as 24 bit images, if there is no alpha channel in the image, you will get dumped down to 16bit (which bands horribly)
If you dont know what i mean by alpha channels, mail me at bigtonenz@ihug.co.nz and i'll talk you through it or do it for you if you dont have photoshop.
Blue