Hi bhenry,
Since Erik's question was posted about 5 years ago, I'm not sure he's still watching the thread. Using VISA VI's in LabVIEW, it is pretty simple to send serial commands over RS-232. It is just a matter of congiguring the resource and performing writes and reads. LabVIEW ships with a few example programs for serial communication that demonstrate how this is done. As far as specific commands to control Lloyd's LRX Materials Testing Machine, you might try their website for any support info.
Good luck,