Small triangles of transparent textures

I am lately having problems with games like Medieval 2: Total war, Shogun 2 :Total war, and Conviction Splinter cell. The thing is that :
-In Medieval2: Total war, when I enter a battle, small parts of the units are missing, triangles to be exact, on the textures. SO, sometimes I get transparent triangles (they look like holes), in the walls of a settlement, on in the very textures of the units.

-In shogun 2: total war, the same things happens, but with the terrain.
-In Splinter Cell: Conviction, the same thing happens with the two soldiers in the main menu. Parts of them look transparent , and some of the textures are sort of streched


Is there any solution to this??
I got an ATI HD Radeon 4300, an a computer with windows 7(64 bits).
EDIT_01: IF you can't see the images, just click on them...