In Outlook 2003 and earlier versons, the closest you can come to a built-in method for sending a calendar as a single file attachment is to export the Calendar folder to a file, then sending the exported file.

However, if you have Word, you can use one of the Word templates listed at http://www.slipstick.com/addins/calendar.htm#print to push the Outlook data into a Word document, then attach that document to a message.

If you have Visio 2003, you can use the Import Outlook Data Wizard to create a calendar from Outlook data, using a filter to include only certain appointments. The resulting .vsd file can then be sent as an attachment.

For VBA code solutions that create an HTML-format mail message containing any single day's appointment list or 30 days of appointments, see:

http://www.outlookcode.com/codedetail.aspx?id=24
http://www.outlookcode.com/codedetail.aspx?id=1227

Another technique is to use a third-part tool called ClipForm (http://www.ivitar.com/clipform/). This tool uses templates to export Outlook data -- a whole folder or selected items -- to the Windows clipboard, text file, HTML email message, or other file types.

Outlook 2007 will make calendar sharing and distribution much, much easier. It will have the built-in ability to generate a nicely formatted email message listing your appointments, with an iCalendar attachment that other Outlook 2007 users can open to add your appointments to a new calendar that Outlook will create for them.