It sounds like what you are wanting to do is set up an extra router (or gateway) as a wireless access point. That can easily be done with most routers.
The pages linked below provide general guidance on how to convert a router to an access point.
http://www.smallnetbuilder.com/basics/wireless-basics/30338-how-to-convert-a-wireless-router-into-an-access-point
http://www.tomshardware.com/forum/36406-43-convert-wireless-router-wireless-access-point
Terms for future use. These are not exhaustive definitions but people here will understand.
Modem. Bridges the incoming wide area network (WAN) line to ethernet.
Router. Connects to a modern and distributes (routes) the WAN to a LAN and usually wifi.
Access Point. Connects to a LAN by ethernet and provides wifi.
Gateway. Usually provided by the ISP and combines modem and router functions in one box and often provides video and phone service too. Often just called a "modem" or a "router" by the ISP because in marketing, the terms are rather loosely used.