To 4rfvgz7tdfght4 and Squirrelinabox (If you still have trouble):
The declaration of FindWindow is wrong, it should look like this:
Declare Function FindWindow Lib "user32" Alias "FindWindowA" (ByVal lpClassName As String, ByVal lpWindowName As String) As Integer
The same is for SendMessage which shold look like this:
Declare Function SendMessage Lib "user32" Alias "SendMessageA" (ByVal hwnd As Integer, ByVal wMsg As Integer, ByVal wParam As Integer, ByRef lParam As Object) As Integer
Long is used in Windows API calls when you use VB6 but not in VB.NET
for Windows API reference for VB.NET.
I have done this myself in VB.NET but I changed to C# when I wanted to make a function that adds tracks to playlist due to problems with pointers.
Hope this will fix your problems.