Computer to computer network password prob

I am trying to set up a computer to computer network via airport between my imac (OS 10.2.8) and my PB (OS 10.3.4). I get to the point where I am asked for the password as a registered user. I have entered every possible password I have on either computer yet it keeps telling me that the password is incorrect. Where is this password set?

Thanks for any help

Now why didn't I think of that??

Thank you. It worked.

Now I can glue back all the hair I pulled out earlier.