Meh... I know what you mean, it's the explaining part that I can't do
Ok... I'd guess the artist used stock image, blending first the background image and the main image together - either by using eraser brushes or layer masks.
Then he/she added on the small images, lowering the opacity so that the background images is visible through it. On top of that, perhaps some adjustment layers like color balance to so that the colors match.
At last, some sparkly and gritty brushing on top of everything. Perhaps.
I'm not sure how much sense that made and I'm sure there were a lot more layers than I can explain here... anyhow, I'm going to write a tutorial on some of my wallpapers this summer
http://www.arwen-undomiel.com/forum/vie ... php?t=9259
It follows pretty much the same concept.
You can also try reading this:
http://www.vrya.net/ts/photoshop9.php
It's more for advanced artists, but I'm sure you can get something out of it. Vrya is one of my favorite artists - some of her wallpapers are so beautiful
edit:
um, just finished writing this too if you're interested
http://www.arwen-undomiel.com/forum/vie ... 837#458837
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