I'm getting 512 as a reading from a thermistor. Trying to convert this into something readable but having a hard time
I believe your problem is that you changed the circuit from the one provided with the thermistor but did not alter the equation. The circuit on the website shows that the thermistor is driven from a 2000 mv (2 volts) source that is adjusted by a pot on the board. That accounts for the 2V factor in the equation relating output voltage to thermistor resistance.  You are now driving the thermistor with 5 volts so the equation must be modified to change the 2V to 5V. You cannot get a Vout of more then 2 volts from the original board.  That is why you are calculating a negative resistance.