All thinkpads have a Wifi card whitelist at the BIOS level that prevent installing certain WiFi cards. The restriction can be bypassed with a BIOS modification: Either installing Libreboot, Coreboot or editing the official Lenovo/IBM BIOS.

In general, this machine works well. It seems impossible to change the wireless card and the builtin wireless card isn't really reliable. It is unclear if it is a firmware problem or just the design of the wireless card, but signal is often weak and the "bars" always look full even if the signal is weak. See also http://www.thinkwiki.org/wiki/Category:X120e