nel form dati....
ho inserito sopra un nuova classe... come mi hai suggerito tu..

Public Class Sql

'mi ricavo il nome del mio DSNName
Dim DsnName As New FrmMain

'è il form che alla connessione chiede user e password
Dim UserPsw As New LoginForm1
Dim user As String = UserPsw.User
Dim password As String = UserPsw.Password

Dim strQuery As String

Dim conn As New OdbcConnection
Public Sub New(ByVal StringDb As String)

'apri il form che mi permette di inserire user e password
UserPsw.ShowDialog(frmDati)

Dim MyConn As String
MyConn = StringDb
conn = New OdbcConnection
conn.ConnectionString = "Dsn=" & DsnName.valore & ";Uid=" & user & ";Pwd=" & password
Dim value As ConnectionState
Try
conn.Open()

value = ConnectionState.Open

Catch ex As Exception
value = ConnectionState.Closed
MessageBox.Show(" Errore di connessione al Database. Controllare i settaggi dell' ODBC ", "Error Database Comunication", MessageBoxButtons.OK, MessageBoxIcon.Warning)
End Try

End Sub

Public Property Query() As String
Get
Return strQuery
End Get
Set(ByVal value As String)
strQuery = value

End Set
End Property

End Class


' classe form dati
Public Class frmDati

.....

End class