We use CVS. While we are given the professional version of LabVIEW, which integrates with source control software, last time I checked, all of the supported software costs money, so we just use Tortoise CVS from outside LabVIEW.
I've introduces two teams to version control, and the most important thing is to make sure there is one person who is the "expert" who has experience with it and can help out. Having multiple people all learning it at the same time doesn't work very well.
LabVIEW does have a compare and merge tool, but it's a long ways from text merging. It's best to avoid mergeing as much as possible. This means making VIs small and only have one person work on a particular VI at a time. We also found it's best to only put one value per global variable vi. If you add a second value to the global variable vi, all VIs in which that global variable vi is referenced will be recompiled.
Hope this helps.
