[lmikle]

Код:

// Expand string by spaces
function SetStrLength(S : String; ALength : Integer) : String;
var
  Sp : Integer;
  I : Integer;
begin
   Sp := ALength - Length(S);
   If Sp <= 0 
     Then Result := S
     Else
        While Sp > 0 Do
        Begin
          Result := '';
          For I := 1 To S Do
            Begin
              Result := Result + S[i];
              If (S[i] = ' ') And (Sp > 0) Then
                Begin
                  Dec(Sp);
                  Result := Result + ' ';
                End;
            End;
          S := Result;
        End;
end;

...
begin
  for i:= 0 to RichEdit1.Lines.Count-1 do begin
  RichEdit1.Lines[i] := SetStrLength(RichEdit1.Lines[i],80);
end;

где-то так.
не проверял.