VB .NET - Verifica se já existe o Registro no Banco de dados

Imports System.Data.OleDb

Public Class Form1

    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click

        Dim con As New OleDbConnection("Provider=Microsoft.ACE.OLEDB.12.0;Data Source=C:\Dados\Cadastro.mdb")

        Dim com As OleDbCommand = Nothing

        Dim queryResult As Integer

        con.Open()

        com = New OleDbCommand("SELECT COUNT(*) FROM clientes WHERE Nome ='" & Me.TextBox1.Text & "'", con)

        queryResult = com.ExecuteScalar()

        con.Close()

        If queryResult = 0 Then

            con.Open()

            com = New OleDbCommand("INSERT INTO clientes (Nome) VALUES (@Nome)", con)

            com.Parameters.Add(New OleDbParameter("@Nome", SqlDbType.VarChar)).Value = Me.TextBox1.Text

            com.ExecuteNonQuery()

            con.Close()

            MsgBox("OK")

        Else

            MsgBox("Este registo já existe")

        End If

    End Sub

End Class

Espero ter ajudado... Abraços!