OK, here goes.
Yes, the XION case you have will work just fine.
Now, if you want to use the
Intel Core2 Quad Q9400 you listed earlier, you will neeed a LGA 775 motherboard. This one would be a good choice:
ASUS P5Q Pro. It's a great overclocker and very reliable.
The
EVGA GeForce GTX 280 you listed requires at least a 550W power supply. If you don't already own a quality high power unit, I would suggest this one:
OCZ StealthXStream 600W Power Supply