When you say it isn't that far from the router, just how far is it?
I have the same BT Hub and it has a range of about 40 feet.
But it is does some to depend on orientation of things - moving the laptop through 90 degrees sometimes makes the difference between no signal and enough signal.
Can you move the router nearer the centre of the house, perhaps?
It seems pointless to be forking out extra for wireless broadband via a dongle when there's a free, faster connection so close.