How do I link two networks via wifi?

I'm running a linksys ADSL modem and wifi router downstairs connecting two wifi laptops to the net. I need to extend the internet connection to the upstairs floor where I have a wired network connected through a simple hub. I want to avoid a wired connection to the upstairs so I thought the best way was to add a wifi access point to the upstairs network and let that communicate with the wifi router downstairs. But then I read that an Access Point cannot communicate with a router. Is that true?

If you want to connect 2 networks wirelessly you need a Bridge on each end. Some AP support bridging. A AP will be good for tying multiple wireless clients.

What make/model of wireless router do you have?
Just curious to look up some specs to see what its capabilities are, depending on what it can do you might not have to buy as much hardware.