Yeah to be honest. If it is only a 300w psu he will probably want to upgrade that then get a card. do you know what his long term plans are?
Best thing to do is to whip the side off (however dell have an awful habit of keeping all the sides stuck together, so you may need to pull the whole case off) and look at the board. It should say on the board somewhere the make and model. Get that and choosing a card is much easier.
As he has 4gb ram, I'm guessing he has upgraded a little as most new machines back then would come with 2gb...so he may no what board he has already
