The procedure that Intel used to reccommend system builders to do was attach
non-resetable sticky backed LCD thermometer strips at strategic places
around the inside of the machine, let it run under worst possible case
conditions, say one fan down and hard drive thrashing for a good while and
then sut it all down and see where the hotspots were in the case.
It has to be said though that Intel provided us with this test strips and I
have no idea where to get them direct, I would imagine google could give
some suppliers for those interested.
Phil