LabView behaves well with multiple versions installed on one machine. Just install the software using the default paths:
LabView 5.1 will end up in C:\Program Files\National Instruments\LabVIEW
LabView 6.0.2 will end up in C:\Program Files\National Instruments\LabVIEW 6
The Start menu will show the different versions. You can create desktop icons for the different versions also.