I forgot my wireless router pword!?

I have a HP running Vista if that matters at all... it is a desktop with a wireless N card (forgot which one, sold in a blue box at Wal-Mart). I had it configured correctly, but then I had to send it in for repairs. During that time I had to reset the router. The router is a Cisco branded one. When I try to connect it asks for a pcode and I can't figure out how to make one or find one or whatnot. The desktop wired to the router is an older one running XP. I have accessed the router but didn't see anything in there that would help.