I run it on a T42 without any problems. I haven't actually run on the T40 but you shouldn't have any problems. I helped someone the other day with a T40 (windoze) and it had a mPCI Cisco wireless card (I don't know if we have drivers for it or not as I am not sure if Genmac supports it) there are drivers for the pcmcia Cisco wireless card but it doesn't handle any encryption. If it has the antennas built in then your best bet would probably be to buy a mPCI wireless card that is supported by Genmac.