Charging 3 AAs in series
No, you can't supply 3.6v! You will need a constant current supply.

I found a great, if not in depth, resource for anything battery related is this site: http://www.technick.net/public/code/cp_dpage.php?aiocp_dp=guide_bpw2_00_toc.

As an alternative, if you can use 5v, you could use a single cell lipo battery and charge it with this neat lipo rider.

Edit

As others have mentioned if you DO use a constant current supply you MUST have some way of monitoring the battery charge state either by monitoring change in voltage or temperature! The batteries will likely explode otherwise.