You may want to download and install the hotfix found here:
http://support.microsoft.com/kb/940105
Quoting NVIDIA:
<quote>The following hotfix is recommended for GeForce 6, 7, and 8 series
customers running 3D applications on Microsoft Windows Vista:
Hotfix for GeForce customers running DirectX 9 and DirectX 10 applications:
http://support.microsoft.com/kb/940105. This hotfix resolves abnormal
application behavior such as crashes and extremely low frame rates when
running some 3D applications at very high graphics settings. This issue is
NOT limited to, but has been most commonly noticed on high-end graphics
cards and the following applications: Battlefield 2, Battlefield 2142,
Civilization IV, Company of Heroes, Half-Life 2, Lord of the Rings: The
Battle for Middle Earth II, Supreme Commander, and Tom Clancy's Rainbow Six
Vegas.
In order for this hotfix to be effective, GeForce customers must also update
to the latest ForceWare Release 163 drivers. <unquote>