This small microcontroller-based circuit will allow the use of a Namco neGcon PSX controller with the PS3, by emulating a SIXAXIS controller. Although originally intended for use with Wipeout HD, it should work for any racing game, although it will not necessarily provide perfect analog control in online games due to lag (see here for more detail).
For information please visit the thread that started it off:
PS3 Negcon - Can it be done? at WipeoutZone.com.