the LV 6.1 example is just calling windows dlls. This VI could be written in any version of LabVIEW. I don't think that it is using anything labview specific that would prevent it from running in LV 5.1
The olny way to convert down is to do a save for previous from LV 6.1, into LV 6.0, and then from 6.0 to 5.1. I know that this seems like a pain, but it is the only way to save it down to your version.
If you haven't seen a new version of LV since 5.1, this might be a great reason to buy LV 8.0. The cost of the new version is less than the amount of time you'll spend finding the old versions, and saving all those VIs for a previous version.
Let me know if you have any questions.
joel