Sync Google Calendar with Microsoft Outlook™ Calendar in Two Directions

Google Calendar Sync allows you to sync events between Google Calendar and Microsoft Outlook Calendar. You'll be able to determine the direction of information flow, as well as the sync frequency. Direction of sync can be 2-way or 1-way specifying either from Google Calendar to Microsoft Outlook Calendar or vice versa. Staying on top of your Google Calendar and Microsoft Outlook Calendar events has never been easier!

http://www.google.com/support/calendar/bin/answer.py?answer=89955