You're also going to have to use a 7805 voltage regulator to power this meter--it won't run off 12V without a negative supply, but it will run off 5V without one.
The 7805 regulator is a three-terminal device available at RadioShack for about 99 cents that takes 12V in and outputs 5V. The third terminal is connected to ground. You won't need to heatsink it for powering this meter. I would solder three wires to the 7805 and then stick it in some heatshrink tubing and shrink it down. Use the TO220 package 7805--this is the only one RadioShack sells.
The resistors needed for a 19.99V full scale reading are 1megohm and 10kilohm. I would recommend the use of 1% tolerance resistors for the greatest accuracy, but you will need to calibrate the meter. I would suggest calibrating it against a digital multimeter.
You will also want to connect the XDP terminal to the DP2 terminal so that the decimal point is in the correct place.
