How to grab files that have the same extension and view them in a list?

Hi,
Well, all you have to do is use the GetFiles method in IO.Directory to get the path and matching extensions in that directory.
VB.NET:

Function GetMatchingExtensions(ByVal Filter As String, ByVal Directory As String, ByVal SearchSubDirectories As Boolean) As String()
        If SearchSubDirectories Then
            Return IO.Directory.GetFiles(Directory, Filter, IO.SearchOption.AllDirectories)
        Else
            Return IO.Directory.GetFiles(Directory, Filter, IO.SearchOption.TopDirectoryOnly)
        End If
    End Function

Call upon this and list everything in listbox by:

For Each file As String In GetMatchingExtensions("FILTER", "DIR", False)
            ListBox1.Items.Add(file)
        Next

Just convert this to C# if you want.
Regards,
iProgramIt