what you were looking at is not 'islamic' origami. They are called tessellations. The photos were tagged with 'islamic' because the artist Eric Gjerde, is often inspired by the geometry inside of mosques. I'm afraid that the world of tessellations is relatively new in development in the origami world, and there are about zero diagrams. But there are a few tutorials on tessellation basics from flickr members like EricGjerde, OrigamiJoel, etc,. Eric is also in the final process of publishing his first book on tessellations to be released this year. (amazon).
Yes I'm sure. But as you learn tessellation techniques, you can figure them out by looking at a photo. There may be some descriptions of Gjerdes techniques in his upcoming book.
Visit http://www.origamitessellations.com , i think it's Eric's website There you can find some instructions on folding tessellations. The easy ones are not that hard to fold, though it could be quite hard for a beginner...