So, apprantly you did no really read the PDF. I just looked at it and found the answers to all your questions. Of the two dip sticks one on the right side and one on the left. The one dipstick has 4 markings on it. Hot - (H)igh, Hot - (L)ow, Cold - (H)igh, and Cold - (L)ow is the transmission dip stick. The other dip stick that has only a (H)igh and (L) marks on it....is your diff dip stick. The PDF has a pictures of the drain plug locations. The picture is kind of confusing, but the diff drain plug looks like its by a Y-pipe of some sort and it looks like its below the drive shaft. Look at page 51 on the PDF to see what I am talking about. Plus, it says to fill the diff with 1.3 US Qts of GL-5 or equivalant diff oil in the guage hole (where you pulled the dip stick out of). Lower the car before you fill it though. Without real pictures that is about as good as I can help.
378awhp/373wtq Custom Dom 3 & CBRD tuned 2006 STI.
"When in doubt...flat out" - Colin McRae