The thing that makes the Duemilanove so nice, from my perspective is that it is pre-assembled. There are lots of clones, like the RBBB, that use the same chip (the Atmega328) and include just the necessary components (crystal oscillator, capacitors, regulator, resistors, etc.) to make a fully functional, after programming, "Arduino".
They are harder to program than the Arduino, though, since extra hardware is required.
The Arduino has several surface mount components that need to be soldered on. Is that within your skill set?
There are enough issues with getting a functioning project going that I would not consider making an Arduino for my first project. Once the first project was working, and my Arduino compatible micro could be substituted, yes.
But, do yourself a favor, and start with a fully assembled and tested Arduino.