Hi,
I'm working to build [hopefully] a multimeter (if not, only an amp meter is necessary) to calculate the current average current. Wondering if this if feasible with a Duemilonova and if so how to start.
Thanks
HI
Of course is possible to do that, but it will be for AC or DC amps meter?
Either way, you will be basically measuring the voltage across a shunt of known resistance and calculating current from there.
Such as these
It will be for DC
Sorry...I'm new at Arduino and electronics 
...so would I be measuring between analog input and ground? Where would the main circuit connect to this? A diagram/description would help.
Thanks thanks thanks
Is the arduino battery powered and otherwise not connected to the circuit with the shunt?
If so, you would connect the arduino ground to the lower voltage side of the shunt and the higher voltage side of the shunt to an analog input (or a voltage divider to an analog input to keep the measured voltage below 5v).
If the arduino ground is connected to your circuit's ground, then you will take connect both sides of the shunt to 2 analog inputs, and use the difference between the 2 readings.
If you could connect the low side of the shunt to ground, then you only need a reading on the high side.