Create a new image in PSP, and make a simple pattern or whatever for your brush. It doesn’t really matter what colour(s) you use because it’s going to end up grey (black/white) anyway.
Click and drag across your image (make sure Feather is set to 0 on your Tool Options box).
Click , and go to your Tool Options box (right-click if it’s not already up). Find the custom brushes and select yours.
Now click ‘Create’, and be careful not to select any of the brushes you want to keep whilst you do this or you’ll delete them.
Now find your brush and use it on an image! If you want to delete your brushes, click ‘Delete’ (under ‘Create’).