The cd-drives are standard across the board. It's just a 5-1/4" expansion bay.
The ATX vs. AT is a standard for the power supplys & motherboards. "Newer" ones are ATX. That standardized the plugs for the power supplies (there are intel & AMD ones now that are specific to the chipsets though). The location of the USB, video, sound and all those other plugs on the back of your computer are in the same general location with ATX. That means any ATX motherboard should fit in any ATX case.
The wattage of the power supply ie: 300W, 350W... 600W, etc. is important depending on how much juice you need. Some video cards grab like 100W. If you're just adding LED's, don't worry. They don't take much. If you have 4 hard drives, 2 DVD drives, and a massive video card, then you need more wattage.
It used to be said that the old T-birds ~1Gig needed a 300W power supply. If I were building a new computer right now, I'd grab at least a 400W. I wouldn't pay more than $60 for a case either:
http://www.microcenter.com/They have plenty of them for that price.