Do you mean a 3D graphics accelerator? And you are quite correct, it is to do with his graphics card. Maybe you could try updating the drivers for your graphics card since your games don't seem to recognise it. Also, make sure you have installed at least DirectX 8.1.
If you want a reasonably priced graphics card, then a GeForce 4 MX440 with 64MB DDR RAM should do, it's about £40 on click here Others might think it's not worth getting the GeForce 4 since it's basically crap according to them but I think it still packs a punch and is excellent for people who are on a budget.
Btw, is it possible for you to give us your PC specifications?