The first diagram is the proper voltage divider ckt to use. The 2nd diagram
will give you "only" 5V readings.
The input voltage range you get depends upon the values of the 2 Rs. As
Rtherm goes less than R, the voltage will tend towards 5V.
As long as the voltage is in the range of 0..5V, you don't have to worry about the
ckt driving too much "current" into the A/D converter pin. However, in general,
you want to use Rs in the range of 1K .. 10K for connection to A/D converter
pins.