The labjack package is included in the Standalone PsychoPy distributions. It differs slightly from the standard version distributed by labjack (www.labjack.com) in the import. For the custom distribution use:
from labjack import u3
NOT:
import u3
In all other respects the library is the same and instructions on how to use it can be found here:
http://labjack.com/support/labjackpython
Note
To use labjack devices you do need also to install the driver software described on the page above