Manufactures HDD Factory Serial Number

[glug]

At the moment im getting the Volume serial number that windows gives you. So every time a pc has been formatted the serial number is different. I'm getting the volume serial number and doing an alogarithm for activation purpose. Every time windows has been installed the serial will be different. this is the code to get the Manufactures Factory serial off the HDD.

 Dim mgmclass As New System.Management.ManagementClass("Win32_PhysicalMedia")

        Dim mgmcoll As Management.ManagementObjectCollection = mgmclass.GetInstances()

        Dim mgmenum As Management.ManagementObjectCollection.ManagementObjectEnumerator = mgmcoll.GetEnumerator

        mgmenum.MoveNext()
        TextBox1.Text = (mgmenum.Current.Properties("SerialNumber").Value.ToString)

The serial number has letters and numbers. I need to convert it to all numbers so i can do the alogarithm. Is there a way i can do this.

Regards
Gerald