The motherboard is in my opinion, the most important part in building a computer. It defines what size case, what CPU, and what RAM or Graphics card you can use. When choosing a motherboard make sure to choose on that is compatible with the CPU that you want to use. Newer motherboards use DDR3 RAM. I would recommend going with one of these because DDR3 prices are dropping. Once you have a motherboard picked out, you can move onto the other parts.