Imports System.Management
Public Class Form1
    Dim objMOS As ManagementObjectSearcher
    Dim objMOC As Management.ManagementObjectCollection
    Dim objMO As Management.ManagementObject

    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        objMOS = New ManagementObjectSearcher("Select * From Win32_Processor")
        objMOC = objMOS.Get
    End Sub

    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        For Each Me.objMO In objMOC
            MessageBox.Show("CPU ID = " & objMO("ProcessorID"))
        Next
        objMOS.Dispose()
        objMOS = Nothing
        objMO.Dispose()
        objMO = Nothing
    End Sub
End Class

Bu şekilde işlemci seri numarasını alabilirsin yalnız visual studio ortamında;
Project > Add Reference > .NET > System.Management Eklemelisin.