Aside from that, I think i know what he's done. And i'm very bored right now so I'm oging to try and copy it and ill let you know whether i was right
edit: ok here's what I got, obviously the guy had more time to play around with burning/dodging/colours but here's a rough attempt
ok really really quickly how i made it in PS:
Get a huge random image, I had a picture of a hotel (it's that random)
Motion blur the image with a similar slant to the wallpaper and at 999 pixels
Use adjustment layers etc. to colour it blue and increase the contrast to make it interesting
Use the warp tool to make it sort of 'splay' outwards from the center, like it does in the wallpaper
Make a new layer and render some standard clouds on to it, then make the layer blending mode to soft light (play around with the opacity, and make a layer mask etc. to make it look pretty)
Play around with the shadows and highlights using the appropriate tools. To alter the colour, I made a new adjustment layer (hue) and adjusted the settings untill the image was green. Then I played around with the layer mask until the very edges were green
New layer, fill it black. add some gausian monochromatic noise through filters, and posterise the image (image>posterise) so there are very few white dots. Set the blending mode to screen.
Duplicate the layer you just made and motion blur it in the same direction as before (only 10px or something)
Your done
I know this is how to make it in PS but hopefully you can adapt it for PSP
