Dim db As Database
Dim rs As DAO.Recordset
Dim rs2 As DAO.Recordset
'Dim mivalor As Integer
'Dim i As Integer
Set db = CurrentDb
DoCmd.SetWarnings False
DoCmd.RunSQL ("DELETE FROM Tabla2")
DoCmd.SetWarnings True
Set rs = db.OpenRecordset("select * from tabla1")
rs.MoveLast
'mivalor = rs.RecordCount
rs.MoveFirst
'For i = 1 To mivalor
Set rs2 = db.OpenRecordset("select * from tabla2")
Do
rs2.AddNew
rs2("Id") = rs("id")
rs2("Adjunto") = rs("Nombre")
rs2.Update
rs.MoveNext
rs2.MoveNext
Loop

Dim db As Database
Dim rs As DAO.Recordset
Dim rs2 As DAO.Recordset
'Dim mivalor As Integer
'Dim i As Integer
Set db = CurrentDb
** borramos los registros de Tabla2
DoCmd.SetWarnings False
DoCmd.RunSQL ("DELETE FROM Tabla2")
DoCmd.SetWarnings True

** abrimos Tabla1
Set rs = db.OpenRecordset("select * from tabla1")

** todo este bloque no vale para nada ya que el movefirst anula el movelast y no usas para nada el recordcount
rs.MoveLast
'mivalor = rs.RecordCount
rs.MoveFirst
'For i = 1 To mivalor

** abrimos la tabla2
Set rs2 = db.OpenRecordset("select * from tabla2")

** Do ... ¿hasta cuándo? ¿cómo se sale del bucle?
Do
** añadimos un registro a tabla2 -bien-
rs2.AddNew
rs2("Id") = rs("id")
rs2("Adjunto") = rs("Nombre")
rs2.Update

** vamos al siguente registro de tabla1, vale
rs.MoveNext

** ¿vamos al siguiente registro de tabla2?   ¿àra qué?      ??????? esto seguro que te casca
rs2.MoveNext

** final del bucle, insisto, ¿cómo se sale del mismo?
Loop

Dim db As Database
Dim rs As DAO.Recordset
Dim rs2 As DAO.Recordset
Set db = CurrentDb
Set rs = db.OpenRecordset("select * from tabla1")
Set rs2 = db.OpenRecordset("tabla2", dbOpenDynaset)
rs.MoveFirst
Do Until rs.EOF
    rs2.Edit
    rs2.Fields(1).Value = rs("id")
    rs2.Fields(2).Value = rs("Nombre")
    rs2.Update
    rs.MoveNext
    rs2.MoveNext
Loop
rs.Close
rs2.Close
Set rs = Nothing
Set rs2 = Nothing

Dim db As DAO.Database
   Dim rs1 As DAO.Recordset
   Dim rs2 As DAO.Recordset
   Set db = CurrentDb
   Set rs1 = db.OpenRecordset("SELECT * FROM Tabla1 ORDER BY Id", dbOpenDynaset, dbReadOnly)
   Set rs2 = db.OpenRecordset("SELECT * FROM Tabla2 ORDER BY Id_REA", dbOpenDynaset)
   If Not rs1.EOF Then
       Do Until rs2.EOF
           rs2.Edit
               rs2.Fields("Id").Value = rs1("Id").Value
               rs2.Fields("Adjunto").Value = rs1("Nombre").Value
           rs2.Update
           rs2.MoveNext
           rs1.MoveNext
           If rs1.EOF Then rs1.MoveFirst
       Loop
   End If
   rs1.Close
   rs2.Close
   Set rs1 = Nothing
   Set rs2 = Nothing