• The datasheet for the ATmega328 (419 pages!).
• Duemilanove overview
• Duemilanove Schematic

This chip has 2K of static ram and 32K of flash memory (and 1K of EEPROM). This means you need to program carefully.

The board can be powered from the USB cable, but also has a jack for an external power supply (7-12 volts) and has a regulator on the board and will automatically switch power sources.

It has an 8 channel 10 bit ADC chip - 6 channels of which are available on a connector on the board. Where did the other 2 channels go? Well they didn't have enough pins for them on the PDIP package used for the Arduino, so you are out of luck. You can configure these pins for digital IO if you need that and don't need the analog inputs. They are named A0 through A5 (this is port C in Atmel documentation). Here is a good discussion of how pins work and how to program them. When set up as outputs, pins can source or sink 40 mA, which is pretty impressive.

There are two other ports (B and D) -- so you might think you would have 16 digital IO pins, and you almost do, there are 14 pins provided on the Duemilanove. Six of these pins have optional PWM capability.

Pin 13 has the on board LED and resistor, so it is a bit tricky to use as a general IO pin, but it can be done.

And there is a serial port! This uses digital pins 0 and 1, so you cannot use these if you are using the serial port.