I'm guessing you mean it's just an "open" wireless network.
If you right click your wireless icon you will see "connect to a network" Just click it and select the network you want and connect. If it's security enabled you will have to enter the pass key.
Back at home just do the same again, select your network, and enter your key if it asks for it. On Vista a "tick box" says for each network, always use this network to connect to, so make sure that's ticked, should be by default.