Yeah well, i'm sure you could replace lights, etc on those cases.
As for specs for a power PC. Anything thats new really
For example, for the video card, most people would choose the 7800GTX (the newest card) and as for the processor, if its for gaming, an AMD 64 of some kind. Though a AMD X2 couldn't go amiss (don't know much about that though).
The sound card would definietly have to be made by creative (No onboard rubbish) like the Audigy series, and the RAM would have to be at least 1GB.
As for the motherboard, one that has PCI-E, and loads of USB 2.0 ports, and features like that.
So, aim high, and you'll probably end up getting top performance