I currently have LabVIEW 5.1, 6, 6.1, 7.0 and 7.1 installed.
The only problem I have is that only one of the versions can be registered to open a VI when double-clicked from explorer. This can be solved by adding all the LabVIEW versions manually to the file types that can open a VI. If this is what you mean when you said "getting confused with libraries", it's something you'll have to look out for.
There's a line you can add to the LabVIEW ini file that will let you specify what version you want registered to open files when double-clicked. Add the line "RegisterExtensions=False" without the quotes to the versions you do not want to run when you double-click on a VI. Change it to True in the one version you do want to open on a duoible-click. Unfort
uately, LabVIEW does not have the capability to look at file to see what version it is and then launch the correct one.
Of course if LabVIEW is already open, whatever file you double-click on will be opened in that version.
The main thing that might cause problems is NI-DAQ. I think the best way to avoid problems here is to first uninstall your current NI-DAQ drivers before installing LabVIEW 7.1 and the NI-DAQ 7.2 that ships with it.
Ed

Ed Dickens - Certified LabVIEW Architect
Lockheed Martin Space
Using the Abort button to stop your VI is like using a tree to stop your car. It works, but there may be consequences.