Sandro, you will have to register your modem online when you get it installed, this is a one time event, the details are stored in the modem afterwards. You should get your registration details in your welcome pack which should hopefully arrive a day or two before the installation date, if it doesn't arrive you will have to phone Customer Service to get the details

Go here now to read how to autoregister online
http://www.cableforum.co.uk/forum/article.php?a=13
The installer will supply the modem, USB and Ethernet cables (plus a Windows CD which is just for Windows/USB connection). It will be up to you to register the modem, the installer will just set the modem signal strengths.
You register the modem using Windows, USB and the CD or alternatively autoregister online without the CD.
Once the modem is registered by either method you can just re-install your OS in the future and your computer will connect.