I need to combine records that belong to "same" account number into one record.

My ultimate goal is to get data that has been exported into excel, into a
word document and do a mailmerge. I would like all data pertaining to Acct#1
in the spreadsheet to merge into the same word document and then all data
pertaining to Acct#2, then #3, etc.....

Is this an Excel question to prepare the data prior to the mailmerge OR is
this a Word question to handle using formulas within the merge?

Help?