Private Declare Function GetEnvironmentVariable Lib _
        "kernel32.dll" Alias "GetEnvironmentVariableA" (ByVal _
        lpName As String, ByVal lpBuffer As String, ByVal _
        nSize As Long) As Long
 
    Private Declare Function SetEnvironmentVariable Lib _
            "kernel32.dll" Alias "SetEnvironmentVariableA" (ByVal _
        lpName As String, ByVal lpValue As String) As Long
 
Private Sub btn_set_Click(ByVal sender As System.Object, ByVal e As _
  System.EventArgs) Handles btn_set.Click
        Call SetEnvironmentVariable("test", param1)    
    End Sub