You can use an old router if you have one as a wi-fi booster,this is a bit more involved and for more advanced users but there are some good tutorials on how to do it that anybody can follow.Here is one form lifehacker: http://lifehacker.com/5563196/turn-your-old-router-into-a-range+boosting-wi+fi-repeater
Here is a very good youtube video on using an old router as a wi-fi booster
You can also use an old router as a wireless access point which is much simpler. Here is a good tutorial: http://www.tested.com/tech/298-how-to-use-an-old-router-to-expand-your-wi-fi-network/
I keep my old routers just for this reason.I have used both of these methods for myself,friends and family.The latter method being much easier and less time consuming.