For this tutorial you are going to need the following plugins:

Filter Factory G
20/20

I have used this picture for this tutorial:

Open this picture in PSP and then go to effects, plug-in filters, filter factory g,
xaggerate and use these settings (I think they're the standard settings)

After applying this filter, your picture should look like this:

It already looks nice enough but we want to use it as a background so we need
to make it seamless........

Open 20/20 and go to images, tile effect:

This is what you should get:

This background is now finished. If you think it is a bit too loud, you can
always tone it down in 20/20 with the option 'muted background'.
:-)