There's a couple of things that may be an issue here. My employer offers wireless packages for our services and I have this issue quite a bit. It is usually environmental and not always a driver
So my first question to you would be where in relation to the router is your windows 7 computer?
The general rule of thumb is to subtract 10 feet of the routers effective radius for every wall and floor between it and the computer. Also ensure that your router is not near a TV, or a cordless phone operating at 2.4ghz on a channel close to or the same as the router. Be aware of duct work if you have central air and electronics in the direct path between the objects. Often times you will find a lot of small environmental factors add up to be one big problem.
Do you also have a lap top available? Try checking signal with another wireless device at the same location the windows 7 rig is at.