Try the following. To prevent confusion between when the user wants to type or drag, the code has been placed in the DblClick() event.
Code:
Private Declare Function SendMessage Lib "user32" Alias "SendMessageA" (ByVal hwnd As Long, ByVal wMsg As Long, ByVal wParam As Long, lParam As Any) As Long
Private Declare Function ReleaseCapture Lib "user32" () As Long
Const WM_SYSCOMMAND = &H112
Const WM_MOVEEX = &HF012
Private Sub RichTextBox1_DblClick()
ReleaseCapture
SendMessage RichTextBox1.hwnd, WM_SYSCOMMAND, WM_MOVEEX, 0&
End Sub