Texture problem

Ok I am not sure if this is a bug or not. Whenever I try to load custom objects into the advanced tourque game engine such as a tree it loads but the textures for the leafs never come out right. I know it has something to do with the alpha transparency because it is either huge black or white spots filling the gaps in the leafs. I have looked all over the fourms for help but the only thing that i could find out was that the alpha textures need to be in png format. But they already are in the png format so I dont see why it should be doing this?If this is not a bug could somone please help me?