Sorry, I'm not familiar with Paint Shop Pro, but there's a good tutorial on masks using Paint Shop Pro here:
http://hometown.aol.com/ronaldlvick/mask1.htm
Basically this is what you need to do to create the effect:
1. Create a duplicate layer. Imagine that you printed your original image on a transparency, and laid this transparency over your original image.
2. Change the duplicate layer to grayscale.
3. Now apply the mask. This is equivalent to selectively erasing the (black and white) picture on your transparency to reveal the coloured picture below. For Paint Shop Pro, you need to tick Edit Mask as well as View Mask.
If you SHOW ALL, it means that the transparency containing your B&W image completely covers the colour original.
If you HIDE ALL, it means that the transparency is completely, well, transparent, and you only see the colour image.
Easier for you to just try this rather than me explaining too much.
Hope it helps.