Major Graphic Glitch (Answer Quick)

When I play all games my graphics really bugs out and it makes parts of the models and world glitch through and makes holes in the ground. I don't know how to fix it so I hope this community can. Here is my computer stats:

Manufacturer: Acer
Model: Aspire X1800
Processor: Intel(R) Core(TM)2 Duo CPU E7500 @ 2.93GHz
2.94GHz
Installed Memory (RAM): 4.00 GB
System Type: 64-bit Operating System



Here is a screen shot from a game called Dragon Nest. I used this game because it glitches out the most on this and it shows the glitch more clearly.