I'm at school, so I can't take any additional pics, but this should show how I did it:
It was pretty easy. I removed the chair portion of the desk chair, then removed the sliders from the Datsun seat. I got some angle aluminum I had laying around, drilled holes appropriately, and used the bolts and holes originally used to hold the sliders on the seat to mount them. The rest is pretty simple if you look at the picture. The fabric is so that the stuff on the bottom of the seat - whatever it is, looks like dead grass or something? - doesn't fall onto the floor.