Zune battery to charge ipod touch?

My plan is to build a minty boost using a zune battery instead. I'm pretty sure i know how to implement the zunes battery to power the LM 7805 5 volt regulator. I need help with being able to chare the zune's battrery... A 3.7 volt Li-Ion Polymer battery. I want to use usb for this. Only trouble im having is how do i get the batter to stop charging when it is fully charged? it has 3 pins; P+, P-, and HDQ. I take it the HDQ has something to do with my problem. also seeing how the minty boost is 3 volts at 500MA my 3.7 volt should work fine as long as i keep the current at 500MA right? Also, I have a Tri-coloed LED (RED, GRN, BLU) I'd like the Red to show up when the zune battery is running out of power and the blue for when its charging the ipod., and green to be on when the zune battery is charging... I know to charge the zune battery isnt going to be far off from how im charging ipod batter with the zune battery. I know this is probably alot to take in so thanks for any help.