You have to install the VISA Run Time Engine on the target machine. It can be downloaded from from NI web site.
If you are using LabView 7/7.1, and if you are only using serial communications. You may enable serial port support during the build-application process (under advanced...),. It will include the few necessary files to do the serial commmunications). If you do that, there is no need to install the VISA Run Time Engine on the target machine