My finished lightbox is pictured above. I did not use PVC cement to connect the pieces, because I wanted to be able to take it apart and store it. I really don't think the cement is necessary, because all the pieces fit together real tight. I also opted not to hang the posterboard backdrop with screws drilled into the frame as the tutorial had. Instead, I took 4 binder clips, and used zipties to connect them on so I could just clip up the backdrop. I figured this way, the backdrop wouldn't tear on the screws. I also could not find T-joints that screwed into the street elbows, so I has to saw off 2 inch pieces of PVC to connect the top pieces. It worked perfectly!
Above are a couple of pictures I took today it it all assembled. As you can see, I am having some lightning issues as everything has sort of a cream tinge to it. The lamps I am using just have regualr 60W bulbs in them. I think I'm going to have to pick up some 6500K Flourescent bulbs or daylight bulbs and see if that helps my color issues.