Hmm, page 12 of this? http://www.formfactors.org/developer/specs/atx2_2.pdf
I was more talking about the cut out for the graphics card, as well as that little part at the top where it's going to screw in. And I did mean to say graphics card I/O in my above post, sorry about that.
I used a GPU cad file in combination with the ATX specification to create the cutout that you see. GrabCAD is a good source of GPU models.