Vista to xp 3g mobile installation problem

Hello,
I just installed Windows XP on a new Lenovo laptop with Vista pre-installed. When I tried to connect my 3 data modem to it I got an install new hardware wizard which couldn't install the hardware because it couldn't connect to the internet - obviously because the hardware was the internet connection - a bit of a chicken and egg situation. After several long phone calls with the 3 helpdesk the conclusion was that the problem was with the operating system and not the modem. They advised me to uninstall XP and reinstall it. I don't know how to do this or even if it can be done. It took 3 hours to install XP in the first place. Any advice would be greatly appreciated as I haven't a clue what to do...