Code:
dim dbconn
dbconn=New OleDbConnection("Provider=Microsoft.Jet.OLEDB.4.0;
data source=" & server.mappath("northwind.mdb"))
dbconn.Open()
should be

Code:
dim dbconn as string
dbconn = New OleDbConnection(configerationManager.connectionStrings("myConn").connectionString)
dbconn.Open()

web.config

<connectionStrings>
<add name="myConn" value="Provider=Microsoft.Jet.OLEDB.4.0;data source=c: the full path to app_Data/northwind.mdb" />
</connectionString>

For help with different DB connection string google it