The next version of the sentry controller board will be here within the next month. For now, it is a "shield" type board, with headers to align with and plug into an Arduino Uno or Duemilanove. That way, the Arduino can handle the RS232 / serial communication with the computer. This is preferable to a 100% homemade board, for now, because the Arduino has a lot of protection circuitry and is known to be very reliable.
Once the board arrives and I confirm that it works, I am considering selling them. See the products page for more details on the board, and pre-ordering.
P.S. sorry for the weird highlighting and coloring on this updates page. I'm having trouble getting the background to be transparent. If anybody has tips, please share. Thanks