That'll be hard... I'd advise not to go past a dual core, if that. The motherboard depends on your CPU, but when you go for a low end CPU generally the motherboard will be cheap. For ram I'd go for a low mhz crosair about 1 or 2 GB DDR or DDR2 (porbs DDR because DDR2 is at around 50-100 dollars, depending on how good you want it to be) and an on board graphics card (this depends on what he is going to use it for, if gaming I would advise at least a nVidia Geforce). If it has to include a screen, you can always go for an old fashion way and look for an analog screen, but the small LCD's won't be too expensive.