Netbook to USB DAC to Headphone Amp on Batteries

Are there any good DACs that I can use with a laptop or netbook, which are either USB powered, battery powered, or rechargeable for at least a few hours?

I am very happy with my Lenovo netbook for traveling, and have a spare 6 cell battery which means I can work and/or listen to music for most of the flight to London.

My Grado headphone amp travels easily and runs for hours on 9 volt batteries.

So all I need now is a good DAC?

Would the HRT Streamer or Musical Fidelity VDAC work this way?

Thanks for any ideas.