Typically if the case exterior is mostly metal with a plastic front, then you would open it up like any normal case. If the case exterior is sheathed in plastic, on the top and bottom of the case there are buttons near the back, you lay it down on the motherboard side and press the buttons. If you press her buttons right, pleasure will^H^H^H^H^H er, ahem, been downloading too much pr0n. Anyways, lay down the case and press the buttons, then the case will open up like a car hood.
Has anyone noticed something about these Dell cases... I've come across a few that were loose so that you didn't even have to push the buttons to open it up. Maybe a design flaw, or maybe people just forced it apart too many times because they couldn't figure it out? Also, what's the deal with the motherboard/case having five slots in the rear? ATX is seven, mATX is four, flexATX is three, miniITX is one... WTF is five???