Hi,first I will check my understanding with you, you want to use FileSystemWatcher to monitor the file in FTP site, don’t you?
Microsoft .NET Framework has introduced classes like System.IO and System.Diagnostics, which contains the FileSystemWatcher class which can raises events when a file is created/renamed/updated or deleted from the specified folder or any other activities.
There is an article talk about how to implement the FileSystemWatcher class using Microsoft Visual Basic .NET detailly.
http://www.codeproject.com/dotnet/folderwatcher.asp
For more information ,you can check following articles
http://www.codeproject.com/useritems/AdvancedFileSystemWatcher.asp
Monitor Multiple Files using FileSystemWatcher
If you have any further questions, feel free to let me know.
Best Regards
Gavin