How can I do to get motherboard and processor serial number in VB6?
I am able to get HD serial number with this code:

Option Explicit
Private Type DRIVEINFO
    HDDSerialNum As String
End Type
Private Sub Form_Load()
Dim objs As Object
Dim obj As Object
Dim WMI As Object
Set WMI = GetObject("WinMgmts:")
Set objs = WMI.instancesof("Win32_PhysicalMedia")
For Each obj In objs
    info.HDDSerialNum = obj.serialnumber
Next obj
End Sub

Can you help me?

The following function gets a WMI object and then gets a collection of WMI_BaseBoard objects representing the system's mother boards. It loops through them getting their serial numbers.

Private Function SystemSerialNumber() As String
Dim mother_boards As Variant
Dim board As Variant
Dim wmi As Variant
Dim serial_numbers As String

    ' Get the Windows Management Instrumentation object.
    Set wmi = GetObject("WinMgmts:")

    ' Get the "base boards" (mother boards).
    Set mother_boards = wmi.InstancesOf("Win32_BaseBoard")
    For Each board In mother_boards
        serial_numbers = serial_numbers & ", " & _
    Next board
    If Len(serial_numbers) > 0 Then serial_numbers = _
        Mid$(serial_numbers, 3)

    SystemSerialNumber = serial_numbers
End Function

The following code gets a WMI object and selects Win32_Processor objects. It loops through them getting their processor IDs.

Private Function CpuId() As String
Dim computer As String
Dim wmi As Variant
Dim processors As Variant
Dim cpu As Variant
Dim cpu_ids As String

    computer = "."
    Set wmi = GetObject("winmgmts:" & _
        "{impersonationLevel=impersonate}!\\" & _
        computer & "\root\cimv2")
    Set processors = wmi.ExecQuery("Select * from " & _

    For Each cpu In processors
        cpu_ids = cpu_ids & ", " & cpu.ProcessorId
    Next cpu
    If Len(cpu_ids) > 0 Then cpu_ids = Mid$(cpu_ids, 3)

    CpuId = cpu_ids
End Function

Only a pleasure. Happy coding...