The closest Outlook 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 a VBA code solution that creates an HTML-format mail message containing
any single day's appointment list, see
http://www.outlookcode.com/codedetail.aspx?id=24 .

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.