Motherboard

The motherboard is basically a tray which all of your components are plugged into.  It is just a big board with lots of connectors which allow you to put in your components.

Which motherboard should i buy?

You should ensure that your motherboard has the right socket to fit your CPU into, motherboards don't support many CPUs, normally only CPUs of the same series (manufacturers make their similar products in series) so make sure the motherboard has the right socket for you.
               Then make sure it has the corect form factor (size) to fit your graphics card into, to be sure and to have room for future upgrades I recommend getting an ATX motherboard, as these will fit any graphics card.
               Next make sure that it has enough DIMM slots for your RAM to fit into and can support as much as you need now and a bit extra for the future, I recommend to get a motherboard with at least 2 DIMM slots and supporting at least 6 GB RAM, as this enables room for upgrades in the future. For more info on RAM go to the RAM page
           The next thing which you need to consider is the PCI or AGP slots.  These are the sockets which your graphics cards go into,  AGP being the oldest, PCI x16 being newer and then PCI 2.0 being the newest, I strongly reccommend getting a motherboard with a PCI 2.0, although newer cards are backward compatiable with the older PCI they will run slower and are completely incompatiable with the AGP.

Integrated peripherals

Often motherboards have integrated components, which are built into the motherboard. These can be called media accelerators or integrated chipsets. These are usually video or sound cards.  For a gamer dedicated sound cards are often fine and only a few choose to replace them. Many are led to believe that using a dedicated sound card will increases performance in games as it takes the sound processing load of the CPU, which it does but barely, the change will be un noticable with at the most a 3 frames per second increase. Which when you spend around £50/ $100 on, isn't really a lot seen as though you can spend that much on a better graphics card boosting your performance considerably.

However integrated graphics cards are a gamers worst enemy, newer ones can play older games from before 2004,  such as counter strike source or call of duty 2. These are good for office work though or a backup video card if the main one fails. Gamers often add another graphics card into a PCI or AGP slot.