AOpen Case and an 9800 GX2?

You will need a true 500W (total) PSU for that card. It's pretty power hungry. I have read about 10 articles on it. When I say 500W, I mean a PSU with at least an 85% efficiency rating, like a decent Antec or Thermalquake PSU. My guess is that your PC with shut off the second you enter into a 3D mode with a 350W supply. For the money, the Antec "True Power" series is very good, and fairly inexpensive. I would probably get the 550W one to be on the safe side. As far as your case, I don't know. That is one long freaking card. If you had like a 7800 in there or something like that before, it will probably be fine. It it's a true ATX full tower or mid tower case, I think it may be tight, but work. I would probably be a little worried about the air flow, though. Honestly, if you have not bought this card yet, I would totally buy an 8800GT for almost a third of the money, and buy a card that will be twice as powerful as the 9800 GX2 in a year in half, two years. It's not worth $650.