iCal Exchange is a free online service that allows you to publich your iCal calendars to the internet for free. When you share your calendar URLs to this service, visitors can download an .ics file (to add to Outlook), or even view your calendar through a Web browser. The web based interface of iCal Exchange allows users to view a calendar in different views such as daily, weekly, monthly and yearly.One can also searchthe calendar online.

I havent tested this but you might be able to use this service with Outlook 2007 that introduces a new feature called Internet Calendar publishing.

Visit iCal Exchange at www.icalx.com