I'm sorry I have never heard of anyone trying this without an exchange server involved. I think the principle here is to share your calendar information with users on different computers. It wouldn't make much since to need to communicate free/busy time with different accounts in the same outlook so it is designed to publish the information somewhere whether it be a file, server, or the internet. That being said it should still be possible to do it. Read this article for more info on the way Free/Busy is intended to work.
http://www.msexchange.org/tutorials/...003-depth.html
Free/Busy information is stored on the server and cannot be cached. Make sure Outlook is "Connected" and not "Offline". Try running Outlook in non-cache mode to see if that helps.
If that doesn't work then I am out of suggestions at the moment, but I will keep playing with it to see if I can replicate your problem and find a fix.