Step 1 :-
First Add shell32.dll to your Project Reference.
* open your project . Then click on Project Menu Item.
* Then click on Add Reference
* Then GoTo Browse Tab In Dialog Box
* In File name copy this line "c:\windows\system32\shell32.dll"
* Click Ok.
Step 2
Now Goto Code Window you can write code written below :-
Imports Shell32 ****
Public Class Form1
Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
Dim shell As New Shell32.Shell *****
shell.MinimizeAll() ******* End Sub
End Class