I have a Lenovo T400 (2767-AK3) bought one month ago.
I have the WiFi AGN card and the performance under linux (ubuntu 8.10) is very bad, in windows is ok.
Also I tried to put a PCMCIA WiFi Card on the top of the card reader but the slot is very tight. I don't want to break nothing and actually I am not quite sure this is a PCMCIA slot. The card is looking like this image