you need a faster video card and more memory.
or try
Go to The nVidia Control Panel and go to Manage 3d settings
Then turn Anisotrophic Filtering OFF
and set Antialiasing Transparency to Multi Sampling
Antialiasing Setting to 2x
Texture Filtering Quality to High Performance
Texture Filtering -Trilinear Optimisation to ON
Texture Filtering -Negative LOD bias to ALLOW
Threaded Optimisation ON
Vertical Sync and Triple Buffering ON