OK, while connected to the router using a cable open a browser and click this link
http://192.168.1.1 then when prompted enter the user name of "admin" and the password of "admin" and you should be logged into the routers admin pages.
Once there click the little plus next to basic on the left hand side to expand it and then click on wireless LAN to bring up the wireless config page. then use the following settings... from the top...
Access point: enabled
channel ID united kingdom and then just pick any channel number (if you get problems with it disconnecting later come back and change the channel)
SSID index: 1
Broadcast SSID: yes
SSID: this is the name used to identify your network that everyone in range will see when they search for wireless networks and can be anything you like.
authentication type: WPA-PSK
Encryption: TKIP
Pre-shared key: this is going to be your password you need for connecting to your wireless, you can put anything you like in here but make a note of it or use something you won't forget.
The rest of the settings below this you can just leave as they are, so scroll down to the bottom of the page and click submit...
Once you've done the above, disconnect the ethernet cable, make sure your wireless is switched on and search for wireless networks, you should see one called whatever you named yours above under SSID, click on that and enter the password you entered above under pre-shared key and you should be good to go.