iCal can be configured to present a list of calendar events for downloading in the iCalendar format. This download will trigger the automatic posting of the event to any application configured to receive this format. The Microsoft Outlook calendar is such an application and will place the event directly on the calendar.
On the Subscription/Outlook Administration menu for any calendar you will find the following:
Checking the box for Enable Microsoft Outlook posting will activate the iCalendar download feature of iCal.
A calendar configured for this feature will have a link placed at the top of the calendar that will produce popup a list of events for the month. The links in this list will download the event in iCalendar format and will auto populate the Outlook calendar with the event. This link can be replaced with a graphic if desired. This is accomplished by checking the box by the graphic you see on the menu. You can supply your own graphic. The graphic used is named icsadd.jpg and is found in the iCal installation folder. This image could be replaced with one of your choice.