hmmm I didn't pick up any sides on to test in what Splatoid said but I can offer you my edition, but what has been said already sounds pretty legit.
okay here goes:
1) Turn off the power, disconnect cables and take your computer to an area you feel comfortable working on it in.
2) remove the panels on both sides.
3) takes the power and IDE cables out of the drive you wish to replace then unscrew the mounting screws and slide the drive out the front, if you don't want to replace a drive then don't do step three.
4) Slide your drive in through the fron of the case in the bay you want it in. It may be easier to use the jumper select before you put it in, either Master, Slave or cable select. Master is usually used for the greater drive IE DVD-RW over DVD-ROM. Slave is for the lesser and keep away from CS.
5) mount your drive with the screws making sure the front plate is flush with your case and then mount it in with the screws.
6) Plug in the IDE cable which is a broad and usually white cable and the four pin molex with 1x Red, 2x black and 1x yellow wires.
7) test it out, it should appear in bios which you can access on boot or in my computer on windows.
8) if everything went well then put the panels back on your computer and enjoy your day.
Installing the optical is one of the easier parts of computer upgrading, even without a guide you should find your way with a bit of logic and good luck.