The update from LabVIEW 6.0 to 6.1 is a purchased update and not available for free. I'm not even sure you can still purchase the 6.1 update since 7.0 has been released. But 7.0 will open any 6.1 and 6.0 files.
6.1 introduced several new features that 6.0 does not support, so it may not be able to be converted back to 6.0 successfully.
You could attach the files you want to try to a message here and post it so some body could try to save them back to 6.0 for you.
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.