Are you talking about the Ipac? If so, I've heard from several reliable sources (including RandyT at Groovy Game Gear) that you should not use the 5v off the ipac.
The power supply on your computer provides 5v power that many people use. Other people cut a wall wart that outputs 5v to provide the power to the p360's.
If not ipac, could you be more descriptive?