Another
Welcome Aboard,
Aussie Jay! I'm still drinking my coffee this morning... running late...
Since our best techie folks haven't posted yet, I'll simply ask for a bit more info:
1. What version of OS X are you running?
2. What model/brand of WiFi router are you using?
3. Have you checked your Keychain to see if it has a record of that password? If you're using a fairly new version of OS X, the app you need to open is Keychain Access. You'll probably still need your Admin password to make the app show the password(s) you used for the WiFi router.
A. Select "Passwords" in the Category list.
B. To the right should be a list of 'places' where Keychain has logged passwords. If you have an Airport base station, it might be quickest to click the "Kind" column and look for "Airport base station" or something similar.
Just to show you how non-techie I am, I have a pretty simple password for our WiFi router, so the five household users can help each other out... usually. I even have it written in the extremely small "manual" that comes with the Apple Extreme! The problem with passwords for things we seldom use is... we seldom have our BRAM* "refreshed"!
*BRAM = Brain Random Access Memory