There's an option within LabVIEW to use native File dialogs or not. If you use the native (OS) dialog, I think you have this functionality. If you de-activate this function, it might restrict as you require.
The only problem is that the LV (Non-native) dialog is a bit ugly. And feels sluggish in comparison.
There may be a possiblity to change the Windows behaviour within
THIS link.
Hope this helps
Shane.
Using LV 6.1 and 8.2.1 on W2k (SP4) and WXP (SP2)