Think AMD when choosing a motherboard and CPU. Make sure the sockets are the same, and make sure you have enough power with your power supply. (A minimal build usually doesn't require anything more than 350-400w). Newegg, Amazon, and ebay are the best places to shop for used, refurbished, and new parts. Just make sure if you buy a used part, it comes with what you need. (i.e.: if you buy a used CPU, make sure it comes with a fan and thermal paste, or you may end up paying more than you would if you just bought a brand new one). For the ram, just get 4gb (Really isn't that expensive anymore, might be even harder to find dual 2gb ram since everything is DDR3 now). For the harddrive, just get 120gb or something crappy. Maybe get some SATA...