The resistance of the thermistor varies in a non-linear manner with temperature, you may need a linearizing circuit.
Convert the resistance to a voltage, an op-amp may be usefull here to allow you to adjust the scaling and zero point of your display.
An A to D converter will be required to digitise the voltage from the op-amp so that it can be displayed on the 7segment LED.
A PIC with an analogue input would be a good way of implementing the A to D conversion and display driving functions.
You may also be able to do the zero, scaling and linearisation in the software in the PIC.
JimB