KNSGEM - Wireless network coverage converter for google earth
http://www.rjpi.com/knsgem.htm
KNSGEM takes Netstumbler Binary files and creates a google earth kml.
Vistumbler is not supported by KNSGEM because it does not create a Binary NS1 file.
However, if you would like to use Vistumbler data in KNSGEM you can export to a Text NS1 file from vistumbler, import it into netstumbler, and save a Binary NS1 file from netstumbler.