Word 07/Outlook 07 Mail Merge

Using a Word mail merge (email) document to send to specific recipients from an Outlook Address book. We are using the CATAGORIES field to distinguish groups, but when we use FILTER & SORT, CATEGORY field is not available in the filter list. Is there a way to get it visible…Im guessing Ill have to use a different unused field to map Category to….something else…?

We have been using a previous version of office, but never set groupings of our recipients. I really didnt want to maintain multiple address books, so was hoping one of these solutions works.