Will the Duemilanove bootloader work in the Uno?
Yes it will.

Both the Arduino Duemilanove and Arduino Uno use the ATMega328P microcontroller. (There is also a version of Arduino Duemilanove ATMega168 that uses the Diecimila bootloader and that is not compatible, so just watch out).

The main difference between the Arduino Duemilanove and the Arduino Uno is that the Duemilanove uses FTDI FT232R IC, whereas the Uno uses the Atmega8u2 microcontroller fto handle the USB to serial UART interface.

Also important is that both boards both have the same 16MHz clock rate.

The schematic for the Arduino Duemilanove can be found here.
The schematic for the Arduino Uno can be found here.

Of course, instead of selecting Arduino Uno as the board type, you need to always select Arduino Duemilanove or Diecimila and the ATmega328 processor.