Are you talking about making a VI modal to another VI or are you wanting it to be modal to all other applications that might be running? If it's the first, could you post a samll example that demonstrates the problem. I use the windows setting all of the time and have never had a problem. If it's the second, then you need to look at the
Windows API Function Utilities (32-bit) for LabVIEW. In there you will find a utility to set any window to be always on top.