The best way is to buy an ADSL wireless router and run a cable to the WAN port.
most people will not like to do such thing as it is a pain.
There are two other hardware that can do the JOB. that I tried from experience and work well.
A) the best way to go buy with "NETGEAR WN2000RPT Universal WiFi Range Wireless Network Extender 802.11B/G/N"
you can find it on the net, its very easy to configure just plug it to the electricity and point out the router you want to it to Extend the signal. high recommend.
B) 2nd one is using your power line to transfer the Ethernet connection, I don't remember the model but we use it for our cables.
but go with option A much better.