It seems like recharging a battery is pretty straightforward. Just apply a DC voltage to the battery : plug +Vcc to Vcc, and GND to GND. We need a diode that makes sure the current only goes from the supply's +Vcc to the battery's +Vcc. That's it.
Now, I am currently looking at a 5V DC/DC converter to get 5V out of pretty much any voltage, it seems. With 2 AAA it should work. The Minty Boost from Lady Ada uses a LT1302. See Minty Boost! - USB charger for your gadgets and http://www.linear.com/pc/productDetail.jsp?navId=H0,C1,C1003,C1042,C1031,C1060,P1029
Though, this setup wouldn't last very long. It is a very nice IC for a small circuit that doesn't use much current, or is not intended to last so long. Also, note that a 7805 5V voltage regulator does heat up when used with a voltage of 7V or more. A DC/DC shouldn't create heat. It think it also doesn't burns Amperes-hours, which makes it a better solution than a 7805.
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