[lmikle]

Вообще, я, например, обычно проверяю в KeyPress

Код:

procedure TForm1.Edit1KeyPress(Sender : Tobject; var Key : Char);
begin
  If Not (Key In ['0'..'9','.',#8,#13,'-'])
    Then Key := #0
    Else
      Begin
         If (Key = '.') And (Pos('.',Edit1.Text) > 0) Then Key := #0;
         If (Key = '-') And (Pos('-',Edit1.Text) > 0) Then Key := #0;
         If (Key = '-') And (Edit1.SelStart <> 1) Then Key := #0;
      End;
end;

Как-то так...