pylibpcap-0.6.1.tar.gz as distributed by sourceforge doesn't include the files constants.c, mk-constants.py, and who knows what else. As such, an attempt to run python ./setup.py build fails with:
pcap.c:2522:23: error: constants.c: No such file or directory
A CVS checkout builds just fine however.
This was fixed in 0.6.2, I think.