All the work I have done with ACT! has been from people leaving it and converting to FM.
I'd imagine based on the data that I was fed for FM, that there is a ton of picky formatting nuances you'll have to calculate in FM to make the data display correctly in ACT.
If you want to at least make the ODBC/ESS sync portion of it a breeze, I highly recommend an existing solution that handles server to ESS/ODBC syncs, like mirrorsync: http://360works.com/filemaker-sync/
Will save you tons of time vs. rolling your own.