Every LabVIEW version only saves in the previous version, so you would need 6.1, 6.0, 5.1, and 5.0 to convert to 4.1.
The main problem is that many features got added with each version upgrade, so it might not be possible to convert everything back if you use any new features in your VI (e.g. event structures).
If the VI is rather simple, it might be easiest to just rewire it in 4.1. You can also post it here, maybe somebody has all versions still installed and can do it for you. (I can currently only go back to 5.1, earler versions are no longer installed).