Micrel 29302 regulator circuit powering a 5v Pocket PC from
a NP-400 7.4v Lithium battery from a Minolta camera.
An approximately 2cm square heat sink is needed for this application.

As a caution, the circuit under load will completely drain the battery if you let it.
This could cause the battery to be out of the charging parameters of the charger.
Equipment designed to use LiIon batteries will shut down at a safe level of battery discharge.