Try writing something like this:

Code:
//////////////// My Edit Box Control settings: ////////////////////
EDITTEXT        IDC_EDIT1,12,88,396,98,ES_MULTILINE | ES_AUTOVSCROLL | WS_VSCROLL
CString	m_EditBoxValue;
DDX_Text(pDX, IDC_EDIT1, m_EditBoxValue);
//////////////////////////////////////////////////////////////////////////

CEdit * eb;
eb = (CEdit*)GetDlgItem(IDC_EDIT1); // Set V

//this is an example

for (int i = 0; i < 1000; i++)
{

   m_EditBoxValue += "New Text ABCDEFGHIJKLMNOPQRSTUVWXYZ Tralalalalalalalalal";

   UpdateData(FALSE); 

   eb->LineScroll(eb->GetLineCount());
Hope, someone finds it useful.