When I receive an invitation via outlook, and then accept it, I get a popup from ACT where I accept it again. It then appears in my ACT! calendar as well as Outlook as I expect.
If my response to the outlook invitation though is "Tentative", then the ACT popup never shows and thus the activity does not show up in my ACT calendar.
According to the online help, I should check off "show tentative activities" on the Calendar preferences tab. There is no such option though on the calendar preferences tab. I have seen discovered that these "advanced" calendar options are only available in the Premium version sof ACT! and not the "Pro" versions. This should be available in ALL versions of ACT! just as it is ALL versions of MS Outlook.