Front Side Bus (FSB) - The Front Side Bus is the most important bus to consider when you are talking about the performance of a computer. The FSB connects the processor (CPU) in your computer to the system memory. The faster the FSB is, the faster you can get data to your processor. The faster you get data to the processor, the faster your processor can do work on it. The speed of the front side bus depends on the processor and motherboard chipset you are using as well as the system clock. For a good read on the workings of your PC in layman's terms, here is the link. http://www.directron.com/fsbguide.html Donald is right. XP would be the most important addition if you're just wanting to up the system to run rebuilder. Even with a slower running PC, XP is needed for handling the larger files.