Jac, i wouldnt worry to much about putting the password back onto your connection, its rare that someone is going to be using your connection etc, but if it makes you feel better, goto this address
http://192.168.1.1 and you should hit your setup page, under wireless settings should be security, in there you can choose to use a passphrase, can be anything you wish, so go ahead and type in a word that you can remember, then click the 'generate' button, this will make a network key for you *(before that, there is a drop down menu, choose WEP as the security option)*
Make a note of the string of alphanumeric code in the box labelled '1' then click the apply, or save settings button (cant remember what its called been a while)
Once you've done that, you should be 99% secure, when windows asks for the security key, enter the string you just jotted down
Hope this helps, oh and you need to be plugged in with a cable to do that, then you can go wireless once again!
If you get stuck, just ask
All the best.
Eddy x