Well the Duemilanove board does have a on-board 3.3vdc voltage regulator supplying the 3.3v pin, but it happens to be mounted inside the FTDI chip and carries a 50ma max output current.
Right, I forgot to say that 3V3 goes away on the Duemilanove board when the USB is
disconnected from the PC. No? Hmmm, I thought the 3V3 went away on mine, but now it
seems maybe I was just loading it too much. ???? 50-mA is nothing. [unfortunately, some
guy borrowed my Duemilanove so I cannot check].