Wi-Fi around the house

Forgive me please for a very stupid question but what experience do people have of wi-fi in old houses with 1m thick walls? Before I get Telecom Italia in to take a look, I'd appreciate some feedback from people who may have done it. We'd obviously position the box somewhere central but does the signal really make it through thick walls or does it, as someone told me, go round walls? (Technology is not my forte, as you can see.)