If you use built-in video on the motherboard, just put in qty 0 for video cards. same goes for sound cards.
Enter your own values in the hand-picked column. These values were calculated from a spreadsheet using voltage and current values, with the exception of the motherboard.
The result is Watts. Over-rate your power supply, meaning, add an extra 50-80W to the power supply's rating to what you calculate here.
Values calculated are peak wattage consumption, such as would occur during heavy gaming.
Excel 2003 spreadsheet version
Check at corsair.com for a calculator that figures out # of HD's and type of graphics card and tells you what wattage of PSU to buy! since expansion is usually inevitable, plan on 2 hard drives and 2 optical drives (total: 4).