How would I build a device using the above sensor to measure the pressure of squeezing my thumb and index finger together? What components would I need? Could this plug into a PC?
You could design a system that achieved the desired readings with a 22kohm resistor, the Virtuabotix 20N Pressure sensor, some wire, and a microcontroller like the Versalino Uno or Arduino Uno. If you want to get your data over USB without having to add a programmer you can use an Arduino Uno, or if you want to have a lot of them and one plug to the computer you should use something like the Versalino Uno to save on cost.
Feel free to let me know if you have any other questions or if there is anything else I can help with.
I look forward to seeing the project you are putting together once it is done.