[alexprey]

эх.

function Replace(strIn, patern: string): string;
 var p,len: integer;
      return: string;
begin
 return := '';
 len := Length(patern);
 p := Pos(strIn, patern);
 while (p >= 0) do
 begin
  return := return + Copy(strIn, 0, p)+patern;
  strIn := Copy(strIn, p+len, Length(strIn));
  p := Pos(strIn, patern);
 end;
 Result := return;
end;

Ну как то так