If you need an immediate notification, WMI is probably the best route. But WMI will also require your process to be running (in a blocked state) all of the time. Alternatively, you could schedule a VBScript to be launched at some interval and it could check each file's last-modified date against a text file or database that you use to store the modification date the last time the script was run.
An even easier solution would be to just check if the modification time changed since the last run. For example, if your script runs every 10 minutes and you discover a file that was changed within the last 10 minutes, report it.
With CreateObject("Scripting.FileSystemObject")
For Each File In .GetFolder("c:\folder").Files
If DateDiff("n", File.DateLastModified, Now) < 10 Then
' File has been modified in past 10 minutes.
End If
Next
End With