I know that Act! can sync using AS, but it will depend on the version you are using (both Act! and ActiveSync).
I also know that there are some issues with syncing Act! with AS 4.1 (and higher).
Hi - I've just installed ACT 2007 (ACT 9.0) and it does sync. However you have to choose to sync with ACT or outlook - you cannot do both. Just a warning also - be very careful installing ACT 9 - you absolutely need to close down any virus software during installation - trust me.