Assuming you are using Word/Access 2002 (let us know which version if you
are not),

If you are trying to use an existing Access database, then when you get to
Step 3 in the wizard, click the Browse... option and select your .mdb as the
data source.

If you are using the "Type a new list" option what happens is that Word
creates a new .mdb with a very specific structure - it has one table called
Office_Address_List and one query called Office Address List. Word gets its
data from the query.

You can open this .mdb in Access, modify the fields in the table in the
usual way, and use either the table or the query as a data source for a
merge, but once you have made structural changes, Word will probably not
recognise the .mdb as an Office Address List any more - you will be led
through a slightly different dialog to select the table/query you want to
use. Also, you can edit the contents of an Office Address List in Word's
Edit Recipients dialog box, but with any other .mdb the Edit button is
greyed out, so you have to use Access to edit the data.

--
Peter Jamieson
MS Word MVP