About all I can contribute is :
many hours of playing with the case.
I can't even begin to guess from seein the front of the case. I usually get a good laugh out of my clients when I have to work on one of proprietary cases. One time, I went to install a CD burner in a clients machines, and the breakdown of time was 45 minutes opening the case, 2 minutes installing the burner, 5 minutes booting and installing the software
About all you can do short of following the advice from the demolition expers above, would be to carefully study the design of the case, and try to see where it might possibly come apart. If that fails, remove every screw you can see,then start prying at the seams with a heavy screwdriver. If it's not held together by screws, there must be clips somewhere. Once you have found the locking mechanism, then it might just be a matter of pushing and pulling in differnet areas until it starts to give.
Best of luck, if all fails, dropping the case from the roof of you house might help, if not, then I'd go for the 20lbs sledge... If that fails, then it's time to get a jackhammer