Well well well, for this tutorial you are going to need:

20/20
Two Moon - Vertical Chop Blur

And for this tutorial I have used this lovely
image:

Open this image in PSP and go to effects, plug-in filters,
two moon, vertical chop blur and use these settings:

Apply them and you should have something like this:

Save this picture, open it in 20/20 and go to image,
tile effect..........and your background is finished :-)