Lol wasn't me who made the mistake pomp, I corrected mark and he edited my post to make me look stupid lol
If you can't be arsed going into the loft....
If you go to internet explorer (or whatever you use) and type in:
in the address bar, and press enter, you will get a username and password information dialog.
Enter admin for the username and leave the password blank
You should get a settings screen.
If you then select 'Wireless' for then click 'Configure WEP'
you will be able to enter a key of your choice (normally a minimum of 6 characters) there.
Take a look here
for more info