Place the VISA Open in a diagram in LV 5.0 and save it, close LV 5.0. Open LV 6.0, then open the saved vi, and you will see the VISA Open in the diagram. However, upon doing this i noticed that OLD has been added to the icon, so i'm not sure if it still works or not. Why not use the VISA Open in LV 6.0?...it can be found in Functions palette>Instrument I/O>VISA>VISA Advanced.
I hope this helps you..
Kim