Marieke,
My company uses Visual Source Safe. For the price (Free with MSDN) it is well worth the money (get it?)
VSS does an adequate job, but is sometimes unreliable (get latest version doesn't always do that, for example) and the user interface is antiquated (Windows 3.x API!) and is extremely difficult to use, and often counter-intuitive. However, given the results, it is certainly better than nothing.
NI uses Perforce. I have not seen it, but I have seen a lot of good features of it, and hear a lot of good things. It is very expensive, but is highly recommended.
Oh, one last thing. LabVIEW has native SCC. Try it out. You may find this adequate, and it's included in the PDS.
Good luck.