Building a HTPC is not unlike building any other computer system, the only real difference is your choice in components. Against popular belief you don't always have to go with the smallest components you can find. In fact any old PC will work.
You do software updates to get the most from favourite programs right? Updating a motherboard BIOS can in a timely manner is also critical. The guide to Flashing a Motherboard BIOS spells out the often complicated steps in plain english. PCSTATS Tips