I did figure out a way to make it work. It involves adding all message
recipients to all sender's contact lists and making sure that the messages
are sent to the recipients in rtf. Here are the detailed instructions from MS:
"I sent a meeting request over the Internet, but the recipient received a
regular message.
Meeting requests are created in Rich Text format, but by default, Outlook
2002 converts them to Internet (iCal) format when you send them over the
Internet. One of the following situations may have occurred.
The request was sent in iCal format, but the recipient is using Outlook 98
or 97, which only support RTF format for requests. Do one of the following:
To reserve RTF format for a request sent to a particular Internet recipient
1. If you haven't already done so, add the recipient as a contact.
2. With the contact open, in the E-mail box, double-click the contact's
e-mail address.
3. In the Internet Format list, select Send using Outlook Rich Text
format."
This remedy specifically refers to Outlook 2002, but it solved my problems
in Outlook 2003. Here's the link to the article, too:
http://office.microsoft.com/en-ca/assistance/ha010347811033.aspx
Good luck!