2010 Mail Merge

You can use Word's Catalogue/Directory Mailmerge facility for this (the terminology depends on the Word version). To see how to do so with any mailmerge data source supported by Word, check out my Microsoft Word Catalogue/Directory Mailmerge Tutorial at:
http://windowssecrets.com/forums/showthread.php/154370-Microsoft-Word-Catalogue-Directory-Mailmerge-Tutorial
or:
http://www.gmayor.com/Zips/Catalogue%20Mailmerge.zip
The tutorial covers everything from list creation to the insertion & calculation of values in multi-record tables in letters. Do read the tutorial before trying to use the mailmerge document included with it.
 
For some worked examples, see the attachments to the posts at:
http://www.msofficeforums.com/mail-merge/9180-mail-merge-duplicate-names-but-different-dollar.html#post23345
http://www.msofficeforums.com/mail-merge/11436-access-word-creating-list-multiple-records.html#post30327
http://windowssecrets.com/forums/showthread.php/157725-Word-2010-Merge-from-excel-into-Table-Directory?p=928391&viewfull=1#post928391
 
Alternatively, you may want to try one of the Many-to-One Mail Merge add-ins, from:
Graham Mayor at http://www.gmayor.com/ManyToOne.htm; or
Doug Robbins at https://skydrive.live.com/?cid=5aedcb43615e886b#!/?cid=5AEDCB43615E886B!cid=5AEDCB43615E886B&id=5AEDCB43615E886B%21566
 
In addition to a 'Many to One' merge, the latter handles:
• Merge with Charts
• Duplex Merge
• Merge with FormFields
• Merge with Attachments
• Merge to Individual Documents
• Merge, Print and Staple