I found a solution that works for me. Outlook 2007 by default uses "Availability Service" to get that information. We're running that but Outlook under CrossOver doesn't seem to find it. Outlook 2003 uses public folders and those work. The following web site is what I followed:
http://www.networkworld.com/community/node/17227
Basically run regedit in your Office bottle and put in:
HKEY_CURRENT_USER\Software\Microsoft\Office\12.0\Outlook\Options\Calendar
Value Type: DWORD
Value Name: UseLegacyFB
Values:0 or not set (default behavior which is to use the Availability Service) or 1 (use Public Folder based Free/Busy information)
When I added that and set it to 1, free/busy started working.
--Rick