Also see this tutorial. -adlabs6
Step-By-Step Weathering 
This tutorial will deal with simple manual weathering techniques which I use, again im certain there are a lot of different way?s to do this. You will be using light gray paint, and dark gray paint, and a square pixel brush , and the softening tool. You can use a squiggly line method or a single pixel method which can be used to show more detail for certain objects. The better your artistic capabilities the more realistic the weathering detail will appear.
In Paint shop Pro you will be working with layers. Make a new layer and call it weathering.
Like this.
FIG.#2
Click on your layers options and the layers properties menu will open as shown above. Name your new layer weathering as shown.
FIG.#3
After clicking ok your new layer will appear in the layer pallet as shown.
Linear Mode
