How can I extend a wireless network?

My fiance and I will be moving into a basement apartment just down the street from my parents house. We aren't going to be able to get high speed internet while we are there, but my parents have said that we can use their wireless internet during the few months we will be there. The signal is a bit weak in the apartment and I was wondering if there is anything that can be used to strengthen the signal like a repeater or something. If there is, could you tell me what I need to look for and maybe a good place to buy one. Thanks!