Macintosh: transfer data from an old HD to a new one

I’d like to transfer data from a hard drive that was in a Macintosh G5 where the motherboard died to an I-Mac. It is my understanding that I need a box of some kind to hold the hard drive, but I also need the applicable cabling to be able to connect it to the I-Mac, which has USB and a Firewire plug in the back, but since it’s “all in one,” it’s not like any other computer I’ve seen where one can slide it in and plug it into the board. In addition, the G5 had a CD-RW that I might like to keep using, if possible.