What do you mean by "sync"?
MSOutlook can publish a simplified version of its calendar in iCAL format to an FTP or WebDav server - and it can import ical files - but this is a very long way from 'sync'ing.
ActiveSync is probably the right tool for implementing integration but a quick google suggests that there is no support for direct iCAL integration (there are products like AtMail - but these only provide a very basic publish capability).
There is at least one shareware program which seems to meet the bill.