If IsNumeric(Textbox1.text) Then
      Me.Text = "Zahlen"
Else
       Me.Text = "String"
End If

    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As _
      System.EventArgs) Handles Button1.Click
        If IsNumeric(TextBox1.Text) Then
            If InStr(TextBox1.Text, ".") Or InStr(TextBox1.Text, ",") Then
                MsgBox("Ist Double oder Single")
            Else
                MsgBox("Ist Integer")
            End If
        Else
            MsgBox("Ist String")
        End If
    End Sub

Try 
test = Integer.Parse(TextBox1.Text)
Catch ex As Exception 
   MessageBox.Show("Keine Zahl") 
End Try

Ralf