The power cable will be identical to the one that feeds power to your DVD/CD drive (and possibly your hard drive if it isn't SATA).
You should be able to pick up, if you do not have an existing lead long enough in your case already, an extender (this is what ATI provide). This has a plug on one end and a socket on the other.
The installation CD....just go to the ATI site and download the driver package, that is all you need and it will be more up to date than a CD
The socket on the card is a molex, usually white. It should be towards the rear of the card (away from where you attach your monitor lead).