To use MSComm or other serial-port programming tools, you'll need:
A USB/serial adapter or chip (FT232 or similar).
A temperature sensor such as a DS18B20.
A microcontroller that connects to the temperature sensor and also has an asynchronous serial output that connects to the USB/serial circuits.
Programming for the microcontroller to read the temperature sensor and send the data to the PC.
Here is one project:http://www.camelspit.org/2008/02/29/envstick-usb-temperature-sensor/
A web search on
temperature sensor usb project
will bring up other examples such as:http://www.poempelfox.de/ds1820tousb/