Re: nVidia GF7600GS temperature sensor via i²C?
All NV4x/G7x GPUs contain a sensor build into the GPU. The sensor and the temperature reading mechanism are inside the GPU. It isn't connected to the i2c-bus. On highend 7800GTX/7900GTX cards and perhaps on some other boards you can find an external sensor chip aswell. This chip is then connected to the i2c-bus.
The nvidia drivers export the temperature using the NV-CONTROL extensions and further there's NVClock which can directly read the temperature from the card. (use nvclock from cvs; the code is a little buggy, I need to add a correct offset for the 7600gs but for the rest it works well)
In the near future nvclock will feature a dbus daemon for hw monitoring purposes, so that external apps can easily read out the temperature, fanspeeds and other parameters.