You have to run a Ethernet wire from the hosting Router the second router. Wire connects to first port on router, not WAN. Usually the company website will tell you how to set it up as a repeater. I don't remember off the top of my head how to setup the IP settings on it, but you can't just plug it in and it work.
But you HAVE to run a wire from the host router to the second router for it to work. The best thing you can do is either start drilling holes for Ethernet, or u can invest in a wireless network card. Simple as that. Unless you want a cord running through your house. Wireless is convenient, because theres no wire to run through the walls, but wireless is less secure, and can often become problematic at some points. I personally would put the extra effort in and start running the wire, simply because you less likely to run into problems with a wire, and the speed is constant.
If running the wire to the router isn't a choice, then you have to go with wireless, which means getting a wireless network card for the comp up stairs.
Just thought.... Wiring a two story house would be kinda hard. So wireless would be the best. You can put both routers in the same room and dramatically improve wireless coverage. Thats what I'm doing with my network. I have a 300N router acting as repeater, and now I'm getting wireless N coverage on a G band, and beside that router I have a 10 dBi antenna connected to the G router.
So the best thing to do is just buy a wireless network card and connect to the router down stairs. Either way money will have to be spent, unless you, again, want that cord running all over the place. If your ok with that, it will work.
Borgslayer
Connect a wireless router to another wireless router?? URGENT 
Linear Mode
