Through trial and error I have slowly figured out some of it. It's a long process though. Surely someone else has a description or tutorial of what part of the .psd goes with which .css style or area?
Comparing the style on the .psd to the .css is also painfully slow. Surely there's got to be someone who has figured out a faster way?
I haven't seen anyone do such a thing. The quickest way to figure it out, would be to create a copy of the main_block image file. Go through on each section of the image and put some text. Then load that file temporarily on your test forum. Then you can look at the text you put in those section to determine where they are when you see it on your forum.