What you need there is a wireless range extender. There are several on the market, but it's probably best if you could find one made by the same people who made your router (they usually play better together, in my experience).

A single extender shouldn't cost more than £30. Some companies even offer small, wall-mounted extenders (about the size of the average plug), if you don't fancy having an extra normal sized router lying around the place.

There are two other alternatives:

1) A second AP set as a Repeater

2) A second AP with the same SSID and encryption key. This is possible, it doesn't do any harm and we use three access points within our building using this method. As far as your laptop is concerned it is the same wireless network and will flick between the different ones as needed.

Connected to the first using Powerline ethernet out of one of the 4 ports on the original router.

The kit I bought allegedly worked in repeater mode but I couldn't get DHCP to work through it. Set them up as above, turned DHCP off in the second AP so that requests would go through to the original one. Seems to work fine with a variety of laptops pdas and phones.

For example:

1 Wired router, connected to 3 Wireless Access Points. Each Acess point uses almost exactly the same settings, the DCHP server should be set to the Wired Routers IP address.

The one difference; overlapping access points must use a different channel, so you use 1, 6 and 11. It gets more complicated with more access points.

And you end up with one ultra big wireless network, which you can roam around in. It's expansive tho, the cheapest I can find 1 Wired Router and 3 Access Points for is well over £100.