Lets see his spec's first. But what I really need to know is what graphics (GPU) does he have now. I believe he has a 350w power supply (PSU) so I would need to see how many amps are on the 12v rail.
Most of the cards out there are using 400w or better PSU's. Some where on the PSU is a sticker and it shows numbers like 3.3v + 13a = 5.0v +17a = 12v +14a something that looks like that.
That way I will be able to recomend a GPU for your father's up grade. Like a HD 6670 or a HD 6770. But I need to know the info on the PSU. I am trying to keep from you having to up grade your PSU as well.