Hi Mike,
In general the best solution for plant-floor installations is to run one our embedded controllers than runs VBAI under our LabVIEW Real-Time OS. Devices like this include the Compact Vision System, Embedded Vision System, and Smart Camera series. All these do not run Windows and tend to be better from a reliability perspective.
If you must use Windows, you'll likely encounter other reasons where running from a read-only system drive has some problems. In general, desktop Windows does not really handle this I don't expect that NI software would be much different in this regard. However, Microsoft does offer solutions for this case, such as Windows Embedded. One of the cool features this has is varying levels of "write filtering" which make writes not persist to the disk drive along with other types of restrictions. You can find out more about Windows embedded here:
http://www.microsoft.com/windowsembedded/en-us/evaluate/windows-embedded-standard-7.aspx
One thing to note is that today NI does not officially support the Embedded line (either XP or Win 7) in most of our products to my knowledge. However, we do have guides available for XP Embedded ( http://zone.ni.com/devzone/cda/tut/p/id/4011 ) and in general Microsoft made the OSes compatible so it is really just up to you to configure it properly to make your particular software work correctly.
Microsoft makes evaluation versions of Win7 embedded available and NI makes evaluation versions of most of our software available, so you could certainly try to create such a system yourself and see if it works for your application.
Eric
