Please be careful:
http://blogs.zdnet.com/hardware/?p=7551&tag=col2;topRated

[...]
We are aware that some customers have reported fan speed issues with the latest 196.75 WHQL drivers on NVIDIA.com.
Until we can verify and root cause this issue, we recommend that customers stay with, or return to 196.21 WHQL drivers.
Release 196.75 drivers have been temporarily removed from our Web site in the meantime.
[...]