The edit box has to be created with the appropriate style to act as a multi-line text box. Look up the styles - off the top of my head I just don't have them memorized. But if the right style wasn't used at creation time - it just ain't gonna ever be a multi-line edit box.
added later - from Api CreateWindow() docs...
ES_MULTILINE Designates a multiline edit control. The default is single-line edit control.
Here would be what a CreateWindowEx() call to create such an edit control would look like...
hEdit=
CreateWindowEx
(
WS_EX_CLIENTEDGE,
"edit",
"",
WS_CHILD|WS_VISIBLE|ES_AUTOHSCROLL|ES_MULTILINE|WS_VSCROLL,
60,80,620,24,
hWnd,
(HMENU)IDC_EDIT,
ghInst,
0
);