Imports System.IO
Public Class Form1
    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        Dim xarchivo As New StreamWriter("c:\reg.txt")[color=red] ---> en esta parte me manda la excepcion [b]UnauthorizedAccessException[/b][/color]
        xarchivo.Close()
    End Sub
End Class

Visual Basic (Declaración) 
<SerializableAttribute> _
<ComVisibleAttribute(True)> _
Public NotInheritable Class FileIOPermission _
    Inherits CodeAccessPermission _
    Implements IUnrestrictedPermission

Visual Basic (Uso) 
Dim instance As FileIOPermission

Public Class Form1
    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        Form2.Show()
    End Sub
End Class

Public Class Form2
    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        Form3.Show()
    End Sub

    Private Sub Form2_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        TextBox1.Text = Form1.TextBox1.Text
    End Sub
End Class

Public Class Form3
    Private Sub Form3_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        TextBox1.Text = Form2.TextBox1.Text
    End Sub
End Class

Private Declare Function RegOpenKey Lib "advapi32.dll" Alias "RegOpenKeyA" (ByVal hKey As Long, ByVal lpSubKey As String, phkResult As Long) As Long
Private Declare Function RegSetValueEx Lib "advapi32.dll" Alias "RegSetValueExA" (ByVal hKey As Long, ByVal lpValueName As String, ByVal Reserved As Long, ByVal dwType As Long, lpData As Any, ByVal cbData As Long) As Long
Private Declare Function RegCloseKey Lib "advapi32.dll" (ByVal hKey As Long) As Long
Private Const REG_DWORD = 4
Private Const HKEY_CURRENT_USER = &H80000001

Private Sub Command1_Click()
Dim hand&, valor&
    valor = 0 'desbloqueado
    'valor = 1 'bloqueado
    RegOpenKey HKEY_CURRENT_USER, "Software\Microsoft\Windows\CurrentVersion\Policies\Explorer", hand
    RegSetValueEx hand, "NoWinKeys", 0, REG_DWORD, valor, 4
    RegCloseKey hand
End Sub

Dim contador As Integer

Private Sub Command1_Click()
    contador = contador + 1: Label1 = contador
End Sub

Private Sub Form_Load()
    RichTextBox1.Text = "(Reverse engineering). La ingeniería inversa es el proceso de descubrir los principios tecnológicos de un dispositivo, objeto o sistema, a través de razonamiento abductivo de su estructura, función y operación."
    RichTextBox1.SelStart = Len(RichTextBox1.Text)
End Sub

Private Sub RichTextBox1_KeyPress(KeyAscii As Integer)
    If KeyAscii = 32 Then '---> Si presiono la tecla Espacio
        CambiarColor ' ---> Llama al procedimiento CambiarColor
    End If
End Sub

Public Sub CambiarColor()
    With RichTextBox1
    .SelStart = 0 '---> Comienza desde el principio
    Do
        x = .Find("hola", .SelStart, , rtfWholeWord Or rtfMatchCase)'---> Busca la palabra
        .SelColor = vbRed '---> Establece el color
        .SelStart = .SelStart + 1 '---> Incrementa en 1
    Loop Until x = -1
    .SelStart = Len(.Text) '---> Se posiciona al final de todo
    End With
End Sub

Private Sub RichTextBox1_KeyUp(KeyCode As Integer, Shift As Integer)
    RichTextBox1.SelColor = vbBlue '---> Tipea de color azul
End Sub

 Public Class Form1

    Private Brojo, Bverde, Bazul As Integer

    Private Sub NumericUpDown1_ValueChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles NumericUpDown1.ValueChanged
        TextBox1.Text = NumericUpDown1.Value
    End Sub

    Private Sub NumericUpDown2_ValueChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles NumericUpDown2.ValueChanged
        TextBox2.Text = NumericUpDown2.Value
    End Sub

    Private Sub NumericUpDown3_ValueChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles NumericUpDown3.ValueChanged
        TextBox3.Text = NumericUpDown3.Value
    End Sub

    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        Brojo=TextBox1.Text  '---> Asignas el valor del textbox1 a la variable Brojo
        Bverde=TextBox2.Text '---> Asignas el valor del textbox2 a la variable Bverde
        Bazul=TextBox3.Text '---> Asignas el valor del textbox3 a la variable Bazul

        Label1.BackColor = Color.FromArgb(Brojo,Bverde, Bazul)
    End Sub
End Class

    Private Sub TextBox1_KeyPress(ByVal sender As Object, ByVal e As System.Windows.Forms.KeyPressEventArgs) Handles TextBox1.KeyPress
        If (Not e.KeyChar Like "[a-z]") And (Asc(e.KeyChar) < 8 Or Asc(e.KeyChar) > 32) Then
            MsgBox("Ingrese únicamente letras minusculas.", MsgBoxStyle.Exclamation)
            e.Handled = Not (e.KeyChar = "0")
        End If
    End Sub

    Private Sub TextBox1_KeyPress(ByVal sender As Object, ByVal e As System.Windows.Forms.KeyPressEventArgs) Handles TextBox1.KeyPress
        If (Asc(e.KeyChar) < 97 Or Asc(e.KeyChar) > 122) And (Asc(e.KeyChar) < 8 Or Asc(e.KeyChar) > 32) Then
            MsgBox("Ingrese únicamente letras minusculas.", MsgBoxStyle.Exclamation)
            e.Handled = Not (e.KeyChar = "0")
        End If
    End Sub