Try the following:
VB Code:
  1. Option Explicit

  2.  
  3. Private Declare Function SendMessageByLong& Lib "user32" _

  4.     Alias "SendMessageA" _

  5.     (ByVal hwnd&, ByVal wMsg&, ByVal wParam&, ByVal lParam&)

  6.  
  7. Private Const WM_PASTE& = &H302

  8.  
  9. Private Sub Command1_Click()

  10.  
  11.     Clipboard.Clear

  12.     Clipboard.SetData LoadPicture("c:\myimage.gif"), vbCFBitmap

  13.     

  14.     Call SendMessageByLong(RichTextBox1.hwnd, WM_PASTE, 0, 0)

  15.     

  16.     Clipboard.Clear

  17.  
  18. End Sub