What is the name of the board and how big is your PSU?
I don't know the name actually but I found this. Is this a name of mother board?
Intel(R) G33/G31 express chipset family
For a old system like that HD7730/50 would be the max card I would recommend, they have low power consumption and will work on 300watt PSU. In all reality the best thing to do is save money and upgrade the whole system.