Photo Mask 101? (or 911?) for PSE 7

[Spatlese]

I absolutely love the look of photo masks that I've seen used in some LO's. I've downloaded a couple of "free" photo masks and was wondering how to use them...is there a quick tutorial somewhere for PSE 7?

I have two formats...one that is in a .jpeg format and one that is in a .png format. The .png is black where I would expect the photo to show through....but I'm at a loss as to how you make that happen!! The .jpeg format is black around the edges, not in the middle, so I can get my photo on it okay, but I can't get that nice transparent look when I try to put it onto a background....it just sits on top like a frame vs a blended & faded out transition....

any help much appreciated!!

thanks