No.... it's not.

Go to your calendar options.... you'll see a button at the bottom called "Free/Busy options". Click that. Under the section called "Internet Free/Busy" check the "publish at my location" checkbox. In BOTH of the dialog boxes under that, put in a location that you and your assistant (and/or anyone else) can see... it's a full filename, but for best practice use a replaceable parameter... something like:

\\OfficeServer\SharedOutlookCalendars\%NAME%.vfb

would put your calendar on the shared OfficeServer, in the subdirectory 'SharedOutlookFolders', and call it something like 'beachrunner.vfb' (well... it'd have your name in there). You put the same thing into the second text field as well and that tells outlook where to look for other people's calendars.

Next, go to your assistant's machine and do the same.... then go to anyone else's machine that you want to share free/busy information with (it's a two way street) and do the exact same for all.

Bingo.... you can all see each others free/busy information, and if an appointment is maked "public" you can even see what the title of the appointment is. No exchange server needed. Only caveat is offline (e.g. mobile) users, but synchronized offline files take care of that too.

Cheers,
D.