While waiting for your suggestions, I found a quick way with the aid of a
powerful text editor (UltraEdit) where I create a URL list with the 808
different URL addresses, all the difference being that they end with an
increasing number. 
This can be done with a text editor that manages Column Mode.

However, I guess there is a simpler solution offered by HTTrack itself, so
thank you to suggest me some filters to create!

Cheers,
Mike