Not too difficult, really. Copying, pasting, masking, rotating, resizing, blending...
Yeah, but you assembled a sleeve from scratch, getting the folds and shading just right. Very nice.
Doesn't look easy to me, but then I'm more of a hack who relies upon being able to find pieces from other images and cannibalize them to fit.
I need to get back into combing through on-line Photoshop tips again... lots of info out there, making it difficult to find what's worthwhile. Any particular tutorials/websites you'd recommend?