What kind of password are you looking for? One for connecting to a particular network? One for accessing this forum? Or, one for using mIRC (aka the registration code)? More details always help.
The first one requires going to the network and registering your nick again. If you don't know how to do that, join the #help channel on the network and ask. The second one would require going to the login screen and click the forgot password link. The third requires doing what RussellB said.
