The regulator on the Arduino is made only for low current output (500mA max, I think), not to mention the Arduino pins should not exceed 20mA or they will most

The regulator on the Arduino is made only for low current output (500mA max, I think), not to mention the Arduino pins should not exceed 20mA or they will most likely burn out. If you are drawing enough current to make the board (I'm assuming, the regulator) go hot, you should be using a bigger external regulator to power the LEDs.