If you already have a PC connected to broadband then you need to buy a ROUTER to split the single broadband connection into multiple connections.
As you want to use a laptop then it is best to go wireless and buy a WIRELESS ROUTER.
Note that if you are virgin CABLE customer you need one type of router (Cable router), if you have Virgin down a normal phone line you need a different type of router (ADSL router).
This may help (it covers XP but Vista may be similar):
http://www.microsoft.com/windowsxp/using/netwo rking/setup/wireless.mspx