On my Mac, I wanted to be able to sync my iPhone with my Outlook calendar without losing my current iCal events and without paying for Apple's MobileMe (although that is certainly a more straight-forward method ).
Granted this method is somewhat a round-about way (but is a completely automated process after a one-time manual setup), but if one doesn't want to lose their current iCal events (via doing the direct Google Calendar to iPhone sync), you can the following steps:
• Install Google Calendar Sync on your Outlook client box.
• Sync Outlook (2003 or 2007 only) with Google Calendar (note: only syncs to primary Google Calendar).
• From iCal app, subscribe to the Google calendar via the "Calendar Settings" (here is a handy tutorial on how to do this).