I'm having trouble downloading Source Filmmaker

I just asked this in the r/tf2 but since it seems all of you guys have it I thought I would have a better chance. I was just given the key to the Beta Access and I clicked to install it but it just said "Source Filmmaker is not available on your current platform."

Now I have a Mac, yes I know, I would like a PC for gaming sometime but I can play tf2 on here anyway. The point is is that someone commented on the last post saying that he heard it can't run on Mac's. Is that true?

Also I'm not closing the Steam "Update News" because I'm not sure if I can get it back or not. I've already taken a screen shot of it just in case it does close on me for some reason. But if it does close is there a way to get it back? I've never really had an "Update News" until now. I'm kind of new to Steam.

Thanks guys, I really appreciate it.