Here we go then!
As you can see, I don't really do an enormous amount of . . . working out, before I start working on something like this (though there were a couple of adjustments to the sketch at the start that aren't captured here, need to remember to save a bit more at the very beginning); I had a pretty good idea of where I wanted them to go and just got stuck right into it.
Done in PS CS4, using pretty much entirely a square brush that can be found here
The final is up here -
(it's a fairly big file, so might take a while to load - be patient!)