To lock your application is not something that is easily done with native LabVIEW code (impossible?).
However, if you are using LabVIEW under Windows you could use the VI I attached below (the VI is written by Shaun Rumbell). It makes an API call and returns the serial number for the drive you specify (e.g. c:\). Use this number to verify that the user is using your program from the machine(s) it was supposed to be used from. Hope this helps. /Mikael Garcia