Firstly, determine your usage for the PC. Then set out the configuration on what you wish to have in a PC, before you source it out. There are things, like the kind of Motherboard (Intel or AMD), Processor speed, RAM (most PC boards can take up to 4GB easily), Hard disk (if you are on databases, then speed is a necessity on large databases for retrieval), type of Graphic card (if you are into graphic designing and this can set you back abit for a good graphic card or Apple is a more desired PC to have with graphics). You also need to decide whether an Apple is more suitable or a Windows one - alot of people swear by Apple, due to the lesser problems with viruses so rampant in the Internet. The list can go on into more intricate details, if desired.