>I aquired a software that compiles
> and protects HTML documents.
>
> It gives the option of protect by
> HD serial number or volume label
>
> I don't understand quite well about this...
>
>
> Which can be changed
>
> The serial or volume label of HD ?
>
> Which is more efficent protection?

Both of them can be changed. The label can be changed very easily. Right click on the drive in the windows explorer, select properties and type new label into "Label:" field. I don't know about any utility to change a serial number but I pretty sure you can find a few by searching on Internet.