I would suggest you pick up a digital thermometer and attach it to your core for ample temp reading.
Not too sure about the PIII operating temps, but I would suggest you don't get over 50C/and I've rarely seen any mobo temp get above 35. Actually 35 was without any case fans at all...but for refrence, my mobo usually sits at 26 - 28C, that's with a 10" house fan blowing in the case though......