An example script for importing a device can be seen below. This script can be executed in the Lansweeper configuration console under Lansweeper\Database Scripts and will add an active printer with the name "Demo Printer" to your database.
You can insert any string in the DeviceKey field, as long as it's unique.
INSERT INTO [tblCustDevices] ([Devicetype],[State],[Displayname],[DeviceKey],[firstseen])
Values (16,1,'Demo Printer','1000',GetDate())