Physically Installing New Hardware

Locating a spare slot (Hardware Cards)

Identify the type of slot you need to install your new hardware into. There are generally three different hardware buses (slots) on today's motherboards :- PCI, ISA & AGP.

If you don't have a spare slot of the type you need you will have to remove one of the other cards in your computer in order to use the new one - not an ideal situation, but an increasingly common problem as people require their computers to perform more and more functions!

If you are installing the new hardware into a previously unused slot you will more than likely have to remove the backing cover from the case before you proceed. This is a metal clip or cover designed to stop dust etc from getting inside the case. They are normally held in place by a single screw or can be 'snapped' out of the casing using pliers. 

Remove the retaining screw and/or unclip the backing cover.

Locating a drive bay (ATA/IDE Hard Drives & CD/DVD ROMS)

Decide where you want the new drive to live.

Most ATA/IDE hard drives are 3.5" form factor whereas most, if not all, CD/DVD Rom drives are 5.25" form factor. It should be evident in the case the bays that are suitable for each form factor.
Some drives will come with a conversion kit which allows you to fit a 3.5" form factor drive into a 5.25" form factor bay.

If you are installing a new hard drive you should put it in a closed front bay (One which cannot be accessed from the front of the PC case). These are usually the 3.5" form factor bays.

If you are installing a new CD or DVD ROM you will need to put it in an open bay which can be accessed from the front of the PC case. These are usually the 5.25" form factor bays.

An open front bay is usually easy to spot by the removable front panel which can be unclipped once the case is open. There may also be a metal trim which has to be snapped off before inserting the new drive. 

CAUTION! - removing this trim can leave sharp edges. Be careful not to scratch the new drive, or more importantly, be careful if you put your hand into the bay to access the drive that you don't remove some of your skin on the sharp edges.
Blood and computer parts don't mix very well!