Yep, I've installed the latest service pack. I've tried doubling the size of the render for png file format, but I get a warning that it'll take too much time, so I scrubbed that. I'm getting really sick of these problems when I've spent so much bloody money on the program sigh

Someone did mention before, though, that they can be saved as .tiff files and then do something with the alpha channels.... I don't understand how that works, so I guess I'm going to have to figure it out.

Thanks everyone :)