Ah, as you're using MS SQL, using the nvarchar will store as unicode so you shouldn't be having the issue. Does it decode correctly when you pull back the data? It could just be that your viewing font doesn't support unicode.
Dim Adapter As New OleDbDataAdapter
Dim Command As New OleDbCommand
Dim xFrom As String = dtpFrom.Value.ToString.Substring(0, dtpFrom.Value.ToString.IndexOf(" "))
Dim xTo As String = dtpTo.Value.ToString.Substring(0, dtpTo.Value.ToString.IndexOf(" "))
sqlQuery = MainQuery ...