Here's an example of how to blend images using Paint Shop Pro 9.
We'll start with two images - one exposed for the foreground, and one for the sky...
1. Open the darker image. <Edit> <Copy> and then close it. You won't need it again.
2. Open the lighter image. <Edit> <Paste... Paste as New Layer>. This will create a new layer visible on the Layers Palette as 'Raster 1'.
3. The 'Raster 1' layer should already be highlighted - make sure it is. Then click on the 'Mask Show All' icon at the top of the palette, which will create a new mask layer and symbol in the same thread as 'Raster 1'.
4. Click on the Background Layer, and then press CTRL+A CTRL+C to select all and copy the layer.
5. Now click on the Mask Layer, and then <Edit><Paste... Paste Into Selection>.
6. That's it, done! All that remains is to right-click on any layer in the Layers Pallette and select <Merge... Merge All> to merge all the layers for the final image.
The result should be something like....
Hope that helps!
