UPDATE - Python version now available at http://netgrab.co.uk/netsleuth-console/
I knocked up a quick tool that I have been using for "portscanning without sending packets" (as per the talks at last years DefCon). It's free download under the GPL and you can get it here.
I have been using it to ID (often Operating System and type) and fingerprint machines of interests during a pentest where I need to be careful not to trigger IDS. The tool can also read .pcap files which I've been using for incident response in analysing data.
It can also read the .pcapdump files outputted from Kismet and has been very useful to me for Wireless pentesting (network broadcast traffic is by far the most common traffic you will be able to see by using Kismet).
I normally have Windows and BT side by side in a pentest. Currently the tool needs Windows, but I am doing a few fixes to make it run natively on Backtrack. The code or installer is available at http://www.netgrab.co.uk/.
Let me know what you think and happy to put your suggestions into the tool.