Any Arduino with built in USB circuitry will never get low enough. You can't disable or sleep the USB side to get anywhere near that amount of time on any reasonably sized battery. When I tried this on my Uno R3 the best I could do was ~30ma
A 3.3v Arduino Pro or 3.3v Arduino Pro Mini could probably be made to go that long with a decent sized lipo. If the previous link looks overly complicated and all you want to do is go low power try the narcoleptic library.
I've got an Arduino Pro lasting about a month on a 1000mah lipo battery with an nrf24l01+ radio and a DHT22 temp/humidity sensor sending updates every 10 seconds over the radio.
It's unlikely 2 x AA batteries will be enough to get you the timeframe you need, with only 2 you'd need boost converter anyway. I would think something like a 2000mah or 3000mah lipo is more what you need to look at. If these nodes will be outside then a solar panel to charge the batteries would give you pretty much unlimited run times.
To give you an idea of where you need to get to, the Pro Mini when asleep with the above hardware attached but powered down uses 70ua. That's 0.07ma. If you can't power down the sensors you're using from the code then you'll need to either run them directly from a digital pin by connecting their VCC to it, or run them via a transister or relay so you turn them off while you sleep. Be aware some sensors takes some time to give valid results after powering up
I think you'd be better off with the above mentioned radios, they are about 1/5th the cost of xbee radios and are likely significantly easier to setup and run