Here are a few links to sites with thousands of masks, you should be able to find one that you like and that will work in fading out the edges of your photo!
http://tubes.ominix.com/art/masks/index.html
http://www.jansdesigns.com/masks.html
Download or unzip into you My Documents/My PSP Files/Masks
Then open the image you want to apply the mask to, making sure you do not work on your original photo, so make a copy or duplicate of it.
Then use Layers>Load/Save Mask>Load from Disk, then a dialog mask window will open and you can choose the mask of your choice to apply to the photo.
Tracey
PS I have a mask applied to my photo avatar above.