The Vista problem in combination with the file NVCPL.DLL is here simulatable on my system:
After the Vista installation and Windows Update (Vista drivers included) no temperature is readable either with your tool nor the NVidia tools. After the installation of the NVidia drivers directly from their website the same results can be observed. After the installation of the NVidia NTune tool the GPU temp is readably from the NTune tool itself, but not from your tool.
The NVCPL.DLL file does have the same file size, version and date from the beginning of the Vista installation until the finalized installation of the NVidia nTune tool.
Within Delphi the LoadLibrary function returns a valid
Handle number, and the ProcAddress is valid obviously too. But the results for the GPU temp as well as the GPU Ambient Temp are always 0. Btw: under XP the GPU Ambient temp returns 0 on all my tested nVidia chips - I don't know if this function is obsolete already.
I have to evaluate this problem in the future to solve it. Especially under Vista.
Soviel auf Englisch.