swapping data on different macs

Hi all,

Apologies if this is already posted elsewhere. I really did look in the forums, I promise.

I'm trying to trade computers with my coworker and don't understand how to switch out data (passwords, preferences, mailboxes and such. I can do basic file swapping). I can only find instructions on how to upgrade to a new computer, and I really don't want to delete the data on either computer in this process. We both are using 10.4.11, one on a mac mini, one on a macbook. We're connected wirelessly, and/or we have an external drive available to help this process. Are there good instructions somewhere, or can someone tell me how to proceed? Thanks!