The 750 seems like a better fit for this computer but one thing is that it also requires a 400w psu and the computer he has currently has a 250w psu. I know that when operating or gaming on a computer and the psu is not enough it can cause random computer crashes and damage even. Obviously don't want that. So would it be best to settle on something lower end for the power supply? Perhaps the corsair series which I believe tend to focus on perfomance and doing the job rather than providing the necessary power for gaming? Its starting to become obvious that a power supply will be needed to.
It "requires 300w", but it will never use more than 75. But it's still going to cut it close on the power supply. I would probably upgrade it to a Corsair CX430 or 500. They're good quality and you can get one for $25 now.