If you're looking for the PC's serial number, you can use WMI. You
need to have admin rights to run this though...
Sub serial()
strComputer = "."
Set objWMIService = GetObject("winmgmts:" _
& "{impersonationLevel=impersonate}!\\" & strComputer &
"\root\cimv2")
Set colSettings = objWMIService.ExecQuery _
("Select * from Win32_BIOS")
For Each objBIOS In colSettings
MsgBox objBIOS.SerialNumber
Next
End Sub