The 15 pin D conn on your laptop is a video monitor port. Most likely unless your laptop is 10 years old it doesn't have a Serial (RS232) port. It should have a few USB ports so use an RS232 to USB adapter to obtain RS232.
There are several on the market that work and some that don't. KeySpan makes a good one.
Another way if you like building is the FTDI chip. SpakeFun sells some on breakout boards.