|Knowing nothing about your particular router models I would suggest you look into dd-wrt firmware. Google that and you'll get an overwelming amount of information. You are trying to turn your second router into and wireless repeater. DD-WRT is capable of that, and can be installed on most routers, but if you screw it up you might kill your router ... for good.|
I've not tried it myself, and can't really help you, but there are many people who have and are willing to give writeups and help over at the main dd-wrt site.