Provided the modem/router is set up properly and working (no error lights):
Wired: just connect an ethernet cable from laptop to router.
below is wifi setup for Windows 7 (I don't have Vista but it's roughly the same):
In Windows, right-click the network icon in the notification area and choose "Open Network & Sharing Centre".
Click "Connect to a network", a small box should appear showing available wireless networks that are in range.
Click your network name, then click "Connect".
If prompted, enter the correct wireless key for that network.
Click 'OK' or "Connect"