Have you tried changing the channel that the router uses to send and receive the wireless signal? There are 13 channels, try choosing a different one in the home hub.
This can be done by accesing the Home Hub page (type 192.168.1.254 into your browser address line), select 'Advanced', then 'Configuration', then 'Wireless' and choose a different channel. The wireless card on the laptop should automatically identify the new channel.
Try each of the 13 available and see if you get a stronger signal - I had a similar problem and found a different channel helped improve the range.
A second option is to use a Homeplug adapter. This is a clever device that uses your home mains electricity circuits as a network. You plug one device into a mains socket (this can be into a multi plug if necessary), and connect it to the router ethernet socket. You plug the second one into a mains socket in the room where the laptop is(or multiplug), and connect it to the laptop ethernet socket (this solution will not use the wireless network card).
The benefit of this approach is that it does not have a range limitation - as long as the second room is in the same wiring circuit, the laptop will connect to the Home Hub as if it was directly connected with a wire.
These Homeplugs can be obtained from various sites (see e-buyer at
http://www.ebuyer.com/product/109683 for �45 + delivery), or you could always ask BT to send you their BT Vision box for �30, it includes a set of these homeplugs and the necessary wires.