As far as getting the images into the mailmerge is concerned, see the
"Graphics from data base" item under the "Special merges" section of fellow
MVP Cindy Meister's website at:

http://homepage.swissonline.ch/cindymeister/MergFram.htm

You are going to run into problems trying to create a catalog type mailmerge
that also contains the name of each individual recipient.

I would suggest that the catalog mailmerge just consist of the list of part
numbers and their image.  In the mailmerge main document, the mergefields
for these should be inserted into the cells of a one row table.  You could
have an extra column in that table for the  quantity.  After executing that
merge to a new document, which will contain a table with a row of data for
each record in your data source, you should then insert a row at the top of
the table into the cells of which you insert headings such as the part
number, picture and quantity and in the cells in the quantity column, you
could insert formfields as used in a protected form, by use by the
recipients in entering the quantity  that they want to order.  You could use
a macro to insert those fields if you want.  Then that document should be
protected for forms, and then you could email it as an attachment to your
recipients, by using the method in the article "Mail Merge to E-mail with
Attachments" at:

http://word.mvps.org/FAQs/MailMerge/MergeWithAttachments.htm