First take an image you wish to place the watermark on

I'm going to use text, so I used the text tool and added the domain name as it belongs here and copied it for many times in a single line.

You take your cursor and when you approach the handles (the little squares around the frame. the cursor will change into a 'bent' arrow. When you see this rotate it as you wish.

Then after, you duplicate the layer for many times as shown above (I suggest you place them in a new 'folder' layer, this will make stuff easier in the final step.

Finally give the layers or folder a very low opacity, I gave it 7%, as you dont want to spoil the image. If everything was done correctly, yo ushould end up with something like above. Here you have the PSD for this tutorial.