The system requirements are:
-Microsoft Windows 98/98SE/Me/2000/XP
-Memory: 128 MB ram
-Graphics card: NVIDIA Geforce series graphics processing unit with 32 MB or ATI Radeon 9000 series graphics card
-Sound card: Directx 8.1 compatible sound card

I only have a couple of recommended specs:
-Graphics card: NVIDIA Geforce 3 or 4 with 64(AGP)
-Sound card: Directx 8.1 compatible sound card

So to answer your question that video card is recommended, but I heard that the Radeon one works better.(You can get more specs at www.playonline.com)
And I don't know how much your score would improve but if I had to guess I would say between 500-800 points because the video card is the most essential part.