[Spynosa]

Puedes usar esta funcion,

Código Delphi [-]
function PadL( sOrigen: string; iLen: integer; cPad: char ): string;
var
   sRet  : string;
   iCont : integer;
begin

   sRet := '';
   for iCont := 1 to iLen do
      sRet := sRet + cPad;

   sRet := sRet + sOrigen;

   iCont := ( Length( sRet ) - iLen ) + 1;
   sRet := Copy( sRet, iCont, iLen );

   result := sRet;

end;

para usarla

Código Delphi [-]
cadena:='10';
cadena:=PadL(cadena,5,'0');