I hope you mean that and not "where do I input it it" because I wouldn't have a clue. Finding it is easy, though - it's in the router's settings so you need to interface with the router using Internet Explorer (or a better browser ) and the address to type in the URL bar can be found as follows:- Go Start>Run in XP or Windows key and R together in Vista or W7 and in the Open box, type
cmd /k ipconfig /all
including the spaces where I've put them. In the black form that follows, look for Default Gateway and note that numeric code down - maybe 192.168.0.1 or similar. That's what goes in IE and you're then faced with a login page. Many routers allow admin as the admin and password or admin as the password and hopefully, yours is one. When you're in, look for Wireless and then Security and note the ten or 26 character code under WEP. Note that it may be hexadecimal so the characters will be 0 - 9 and a - f. - no Os or Is to confuse the issue.