Thank you for your post.
I'm not familiar with ACT!, so I'm not sure what you mean by your "to do lists". Is this in iCal? If so, you'll have to export the iCal data. FileMaker Pro will not integrate with iCal directly.
Bento is a personal database that works only on Macintosh Leopard OS (10.5.x) and integrates with both Address Book, iCal and Mail. You do not need to purchase Bento.
Let me know if you have any additional questions or need clarification for any of the above statements.