Dorian,
Having worked in several multi-developer LabVIEW situations, I HIGHLY recommend Perforce.
Perforce is a revision control system application that costs $600 per user. You'll need some space on a central server to store all the depot VIs and other files. LabVIEW 6.1 PDS supports the interface to Perforce directly so you can check-in and check-out VIs as you edit them.
Check it out at www.perforce.com.
BTW - last I heard, NI uses Perforce for its own VIs and even for LabVIEW itself.
Cheers,
Daniel L. Press
PrimeTest Corp.
www.primetest.com