Can I exchange meeting requests with people who work at another company and who might not use Outlook? I see a When sending meeting requests over the Internet, use iCalendar format option, but it's disabled.

You're on the right track because iCalendar is the Internet standard for exchanging meeting requests with applications other than Outlook. The option you describe is available in Microsoft Office Outlook 2003 and Outlook 2002 and appears in Tools, Options, Calendar Options, but it's disabled unless the user has an Internet mail account in his or her mail profile. Fortunately, despite the disablement, Outlook can use iCalendar format even if you don't send a meeting request from an Internet account. Exchange Server 2003 and Exchange 2000 Server automatically send meeting requests to Internet recipients as iCalendar messages. If you use Exchange 2003 or Exchange 2000 as your mail server, you need do nothing special in Outlook to ensure that your meeting requests go out as iCalendar messages to people outside your organization.

Exchange Server 5.5 is another story, however. It doesn't seem to be able to generate iCalendar meeting requests at all. A workaround exists for recipients who use Outlook: Double-click the recipient's email address either in the outgoing message or in the recipient's contact record, then select the Send in Outlook Rich Text format option. This action forces the outgoing meeting request to travel as an Outlook item, with a winmail.dat file containing the Outlook-style meeting request. The Outlook recipient receives a full-blown meeting request with the same Accept and Decline buttons that you see when responding to a meeting request from someone inside your own Exchange organization. To send an iCalendar invitation to someone who doesn't use Outlook, you must switch Outlook to a different profile that has only Internet accounts, and no Exchange 5.5 mailbox, so that you can use the use iCalendar format option.