I didn't even notice that it was for PSP.
Just a wee simplification of Welles suggestion.
After opening the image you want to use as the edge mask:
1 Select All then Copy.
2 In your working image, add a mask.
3 Alt+click on the mask thumbnail and paste.
4 Command+T and scale to fit.
Back in the Layers Palette, click on the image thumbnail to view.
This method opens the greyscale mask channel directly.
Watch the Channels Palette to see what is happening.
Create your own greyscale edge patterns at a fairly high resolution and you can just scale down without really affecting the definition as you might get when scaling up.
You can always run the G-Blur, or even sharpen it for that matter.
Just work on that greyscale channel directly.
Experiment, that's where the fun is. Try copy/ pasting a whole image directly into the mask and see what happens.
Did I mention something about a wee simplification somewhere?
That Alt+click on the mask thumbnail is really handy, honest.
Cheers, Al.