Making a good detail texture in Photoshop

Hi all,
I've been trying to do this tutorial right here: http://www.guildofwriters.com/wiki/Detail_Texturing
However, when it comes to knowing how to make a detailed texture in Photoshop to use for mipmaps, I am absolutely clueless.
How do you make a texture like this in Photoshop? Does it need an alpha layer?
Thanks!
I've been trying to do this tutorial right here: http://www.guildofwriters.com/wiki/Detail_Texturing
However, when it comes to knowing how to make a detailed texture in Photoshop to use for mipmaps, I am absolutely clueless.
How do you make a texture like this in Photoshop? Does it need an alpha layer?
Thanks!