Because I did not like the way that Access handled the screen real estate, I
went back to 2003 on this machine, but I am sure that somewhere in Access,
there will be the facility to initiate a Mail Merge with Word as there is
under the Tools menu in 2003.  Using that will allow you to avoid the
connection to the data source properties that you can experience in Word if
the connection method is not suitable.

In Word 2007, to be given the option of the way in which the connection to
the data source is made, click on the Pizza Button and then in the bottom
border click on Word Options and then go to the Advanced item and scroll
down to the General section and check the box for "Confirm file format
conversion at open".

Then when you go to attach the data source to the Mail Merge main document,
you will be given a choice of the method by which the connection should be
made.