It took me a bit, but I finally got Kismet installed and running on my Thinkpad T40. I believe the on-board wireless chip is a Cisco, and as such was not easily detected. There were a couple of things I needed to fix.
Mainly, I had to edit the read-only kismet.conf file.
In the file, there were two settings that needed to be changed. The first was the user Kismet would drop into if needed. I run Ubuntu, and to get Kismet to work properly, I start it with sudo. Secondly, you need to add a source record. This was the hardest part for me. A quick check at the ThinkWiki showed me that the wireless card could have been one of three manufacturers. A little trial and error got me to the Cisco card (and even that had some tricky conventions.) In my case, I set the source = "cisco_wifix,eth1:wifi0,Cisco" That middle parameter was the tricky part. For the Cisco card, you have to list both configurations. You can get a listing of the different chipsets and parameters at Kismet's documentation page.
To get Kismet running, I just typed 'sudo kismet' and away I went.