Aki pongo el codigo para el llenado (despues de tanto pesar)
<%@ Page Language="VB" Debug="True" %>
<%@ import Namespace="System" %>
<%@ import Namespace="System.Data" %>
<%@ import Namespace="System.Data.OLEDB" %>
<%@ import Namespace="System.Data.OleDb.OleDbException" %>
<script runat="server">
SUB PAGE_LOAD(obj As object, e As eventargs)
If Not (Page.IsPostBack)
RELLENA_DDLPROGRAMA()
else
descripcion()
end if
END SUB
SUB RELLENA_DDLPROGRAMA()
' ---- CON ESTE RELLENAMOS EL DEL PROGRAMA ----
Dim strConexion As String
Dim objConexion As OleDbConnection
Dim objComando As OleDbDataAdapter
Dim objDS As New DataSet
strConexion = "PROVIDER=MICROSOFT.JET.OLEDB.4.0;DATA SOURCE=" & Server.MapPath("db/tabla.MDB")
objConexion = New OleDbConnection(strConexion)
Dim objSelect as String = "SELECT * FROM PROGRAMAS;"
objComando = New OleDbDataAdapter(objSelect, strConexion)
objComando.Fill(objDS, "PROGRAMAS")
Dim Row
Dim I As Integer = 1
drop1.Items.Add("Seleccione")
drop1.Items.Item(0).Value = 0
For Each Row In objDS.Tables("PROGRAMAS").Rows
drop1.Items.Add(Row(0))
drop1.Items.Item(I).Value = Row(0)
I += 1
Next
objConexion.Close()
END SUB
SUB RELLENA_DDLSUBPROGRAMA(sender As System.Object, e As System.EventArgs)
' ---- CON ESTE RELLENAMOS EL DEL SUBPROGRAMA ----
call DESCRIPCION()
Dim strConexion2 As String
Dim objConexion2 As OleDbConnection
Dim objComando2 As OleDbDataAdapter
Dim objDS2 As New DataSet
strConexion2 = "PROVIDER=MICROSOFT.JET.OLEDB.4.0;DATA SOURCE=" & Server.MapPath("db/tabla.MDB")
objConexion2 = New OleDbConnection(strConexion2)
Dim objSelect2 as String = "SELECT CV_SUBPROGRAMA FROM SUBPROGRAMAS WHERE (CV_PROGRAMA = '" & drop1.SelectedItem.Value &"') GROUP BY CV_SUBPROGRAMA ;"
objComando2 = New OleDbDataAdapter(objSelect2, strConexion2)
objComando2.Fill(objDS2, "SUBPROGRAMAS")
Dim Row2
Dim I2 As Integer = 1
drop2.Items.Clear
drop2.Items.Add("Seleccione")
drop2.Items.Item(0).Value = 0
For Each Row2 In objDS2.Tables("SUBPROGRAMAS").Rows
drop2.Items.Add(Row2("CV_SUBPROGRAMA"))
drop2.Items.Item(I2).Value = Row2("CV_SUBPROGRAMA")
I2 += 1
Next
objConexion2.Close()
END SUB
SUB RELLENA_DDLSUBSUBPROGRAMA(sender As System.Object, e As System.EventArgs)
' ---- CON ESTE RELLENAMOS EL DEL SUBSUBPROGRAMA ----
call DESCRIPCION()
Dim objDS3 As New DataSet
dim strConexion3 as string = "PROVIDER=MICROSOFT.JET.OLEDB.4.0;DATA SOURCE=" & Server.MapPath("db/tabla.MDB")
dim objConexion3 = New OleDbConnection(strConexion3)
Dim objSelect3 as String = "SELECT CV_SUBSUBPROGRAMA FROM SUBSUBPROGRAMAS WHERE ((CV_PROGRAMA = '" & drop1.SelectedItem.Value & "') and (CV_SUBPROGRAMA = '" & drop2.SelectedItem.Value & "')) GROUP BY CV_SUBSUBPROGRAMA ;"
dim objComando3 = New OleDbDataAdapter(objSelect3, strConexion3)
objComando3.Fill(objDS3, "SUBSUBPROGRAMAS")
Dim Row3
Dim I3 As Integer = 1
drop3.Items.Clear
drop3.Items.Add("Seleccione")
drop3.Items.Item(0).Value = 0
For Each Row3 In objDS3.Tables("SUBSUBPROGRAMAS").Rows
drop3.Items.Add(Row3("CV_SUBSUBPROGRAMA"))
drop3.Items.Item(I3).Value = Row3("CV_SUBSUBPROGRAMA")
I3 += 1
Next
objConexion3.Close()
END SUB
SUB DESCRIPCION()
Dim DS1 As New DataSet
dim DS2 as new DataSet
dim DS3 as new DataSet
dim strConexion4 as string = "PROVIDER=MICROSOFT.JET.OLEDB.4.0;DATA SOURCE=" & Server.MapPath("db/tabla.MDB")
dim objConexion4 = New OleDbConnection(strConexion4)
' Esto es para cuando cambia el primer dropdownlist
Dim Desc1 as String = "SELECT DESCRIPCION FROM PROGRAMAS WHERE (CV_PROGRAMA = '" & drop1.SelectedItem.Value & "') GROUP BY DESCRIPCION; "
dim Comando1 = New OleDbDataAdapter(Desc1, strConexion4)
Comando1.Fill(DS1, "PROGRAMAS")
Dim DesPro
Dim I4 As Integer = 1
For Each DesPro In DS1.Tables("PROGRAMAS").Rows
txtMsg.text = " "
txtMsg.text = DesPro("DESCRIPCION")
I4 += 1
Next
' Esto es para cuando cambia el segundo dropdownlist
if not(drop2.SelectedItem.value = "Seleccione") then
dim Desc2 as string = "select DESCRIPCION from SUBPROGRAMAS Where ((CV_PROGRAMA = '" & drop1.SelectedItem.Value & "') and (CV_SUBPROGRAMA = '" & drop2.SelectedItem.Value & "')) group by DESCRIPCION; "
dim comando2 = new oledbdataadapter(Desc2, strConexion4)
comando2.fill(DS2, "SUBPROGRAMAS")
Dim despro2
dim i5 as integer = 1
for each despro2 in DS2.Tables("SUBPROGRAMAS").Rows
txtMsg.text += " "
txtMsg.Text += despro2("DESCRIPCION")
i5 += 1
next
end if
' Esto es para el tercer dropdownlist
if not(drop3.SelectedItem.value = "Seleccione") then
dim Desc3 as string = "select DESCRIPCION from SUBSUBPROGRAMAS Where ((CV_PROGRAMA = '" & drop1.SelectedItem.Value & "') and (CV_SUBPROGRAMA = '" & drop2.SelectedItem.Value & "') and (CV_SUBSUBPROGRAMA = '" & drop3.selecteditem.value & "')) group by DESCRIPCION; "
dim comando3 = new oledbdataadapter(Desc3, strConexion4)
comando3.fill(DS3, "SUBSUBPROGRAMAS")
Dim despro3
dim i6 as integer = 1
for each despro3 in DS3.Tables("SUBSUBPROGRAMAS").Rows
txtMsg.text += " "
txtMsg.Text += despro3("DESCRIPCION")
i6 += 1
next
end if
objConexion4.Close()
END SUB
</script>
<html>
<head>
</head>
<body>
<form runat="server">
<p>
<asp:DropDownList id="Drop1" runat="server" AutoPostBack="True" OnSelectedIndexChanged="RELLENA_DDLSUBPROGRAMA"></asp:DropDownList>
</p>
<p>
<asp:DropDownList id="drop2" runat="server" AutoPostBack="true" OnSelectedIndexChanged="RELLENA_DDLSUBSUBPROGRAMA" >
<asp:ListItem>Seleccione</asp:ListItem>
</asp:DropDownList>
</p>
<p>
<asp:DropDownList ID="drop3" runat="server" AutoPostBack="true">
<asp:ListItem>Seleccione</asp:ListItem>
</asp:DropDownList>
<asp:TextBox BorderWidth="1" Columns="100" ID="txtMsg" MaxLength="100" ReadOnly="true" runat="server" TextMode="SingleLine"></asp:TextBox>
</p>
</form>
</body>
</html>
dropdownlist 
en que momento se lo pasas..
Alguien que sepa como se le hace para poder llenar 3 dropdownlist pero restringiendo los datos a la seleccion del 1o para el llenado del 2o y restringir los datos del 2o para llenar el 3o... por favor... 
