If you don't see a switch on the outside case, there probably is not one. My T61p switch is on the front left edge, but that is a newer enhancement on Thinkpads, and I don't recall that the R51 has one. You would have to go to the Lenovo Support site for your specific model (nnnn-aaa) and download the hardware manual.
I left a link above to find the drivers for your card. Most likely the V 4.1.2. 56 version will work, but you need to look through those drivers and match your card and OS. I don't know of any other source at this point.
Also, find or buy a short ethernet cable and plug your R51 into your wireless router to make sure something unrelated is not wrong. ... Thinkpads_User