Hey PJ,
If you want to play any decent games you will want to purchase a discrete graphics card instead of using the integrated graphics memory on your motherboard. Integrated graphics are ok for running vista and watching some lower resolution videos--but to watch HD video or to play games you really want to purchase a graphics card. It may also help speed up the rest of your computer--as your ram will no longer have to share with the graphics.
Depending on what kind of games you are talking about, you could significantly boost your visual experience by adding a low-end card for as little as $30-40.