Outlook doesn't support importing to a custom fields. You'd have to write custom code or use a third-party application. See http://www.outlookcode.com/d/customimport.htm.
And how well Business Contact Manager would support those fields is a completely matter that you might want to take up in the microsoft.public.outlook.bcm newsgroup.

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Sue Mosher, Outlook MVP
Author of Configuring Microsoft Outlook 2003
http://www.turtleflock.com/olconfig/index.htm
and Microsoft Outlook Programming - Jumpstart for
Administrators, Power Users, and Developers
http://www.outlookcode.com/jumpstart.aspx
>I have created my own field names in Business Manager, however when I attempt
> to import the data from either an MDB or Excel spreadsheet, the option to
> import my field names is not there.
>
> How can I import field names that are not in the list of fileld names
> offered ?