try using just this code to see if you get notifications of button presses when you press one of the A,B,X,Y buttons.

Code:
Imports Microsoft.Xna.Framework
Imports Microsoft.Xna.Framework.Input

Public Class Form1

    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load

        Dim ControllerTimer As New Timer
        ControllerTimer.Interval = 100
        AddHandler ControllerTimer.Tick, AddressOf TimerTick
        ControllerTimer.Start()

    End Sub

    Private Sub TimerTick(ByVal sender As Object, ByVal e As EventArgs)

        If GamePad.GetState(PlayerIndex.One).Buttons.A = ButtonState.Pressed Then
            MessageBox.Show("A button")
        End If
        If GamePad.GetState(PlayerIndex.One).Buttons.B = ButtonState.Pressed Then
            MessageBox.Show("B button")
        End If
        If GamePad.GetState(PlayerIndex.One).Buttons.X = ButtonState.Pressed Then
            MessageBox.Show("X button")
        End If
        If GamePad.GetState(PlayerIndex.One).Buttons.Y = ButtonState.Pressed Then
            MessageBox.Show("Y button")
        End If
    End Sub

End Class