Do Outlook contacts have a place to store an account number that a Microsoft Word mail merge form letter can include as a reference number?

Yes, you'll find an Account field on the All Fields tab, under Outlook's All Contact Fields. For an easy way to fill in the Account field for many contacts, display the Phone List view in your Contacts folder and add the Account field to that view. To do so, right-click the column headings, choose Field Chooser, and drag the Account field from the All Contact Fields list to the column headings. Because the Phone List view is set up by default for in-cell editing, you can click in the cell under Account for each contact to type in the account number.

The Microsoft article "How to tell the difference between field names in an Outlook 2003 contact list and in a Word 2003 mail merge" (http://support.microsoft.com/?kbid=818851) provides a guide to the built-in Outlook fields that are available to a Word mail merge and how they match up with the names displayed in Word's mail merge field lists. Although the article is specifically for Microsoft Office Outlook 2003, the field lists in Outlook 2002 should be the same or nearly so. Note that Office 2003 Service Pack 1 (SP1) fixes a problem in which the ZIP Code/Postal Code field might not work properly in mail merge.