There are about a zillion different ways to do this. You could use a data control and bind the text boxes to the database field names, but I intensely dislike bound controls, so I won't suggest that. If this does interest you however, there are many examples of how to do this in nearly everybook on beginning VB programming.
A better way would be to build a recordset based on an SQL call in which you SELECT all of the fields in your table that you want for Customer=Trim(cboCustomer.Text)
If you build your recordset on this SQL statement: SELECT firstname, address, city, state, zip FROM YourDatabaseName WHERE Customer=Trim(cboCustomer.Text)
Then, you can write a series of If/Then statements such as:
If IsNull(rs.Fields("firstname"

) Then
txtfirstname.Text = ""
Else
txtfirstname.Text = rs.Fields("firstname"

End If
Where rs=the name of your recordset, and firstname is the name of the First Name field in your db table.
There is a much nicer, tighter way of populating your text boxes, but this will work. If you are interested in something a bit more sophisticated, let me know.