The datasheet for the 945GME says that there are two thermal sensors on the chip, which can be configured through MCHBAR registers.
Setting TSE (Thermal Sensor Enable) to 1 in the TSC (0 or 1) register does not seem to have any effect. The Thermometer Mode Output Valid bit in the TSS register will remain zero and the TR register will continue to read FFh. Other bits (e.g. lock bits) work as advertised, so I'm pretty sure I'm accessing the right regs.
This is on a D945GSEJT board with Ubuntu 10.10 (kernel version 2.6.35) and a kernel module to access the MCHBAR register space (using the mapping already set up by the i945 module).