iSync is for syncing the computer and a mobile phone (of the non-smartphone variety), it doesn't sync between computers.
There are various solutions. The cheapest and simplest solution is to use Google Calendar (calendar.google.com). There you can create calendars and share them, and iCal integrates very nicely with Google Calendar. Create an event in iCal and is automatically synced with Google, and form Google to all your computers and smartphones. It works fantastically, and your calendar also becomes accessible from the web (you can even share free/busy info with others).
The next easiest, but at a cost of $99/year is using MobileMe. Apple has syncing with their MobileMe service in each of their contact, e-mail, and calendar apps. It works well, but only works well with MobileMe-enabled apps.
Finally, if you install OS X server on a Mac in your home, you can setup OS X calendaring services, which provides synchronized calendaring to all the machines on your network.