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See: http://www.dirk-loss.de/scapy-doc/installation.html#installing-scapy-v1-2 for more info.
Copy scapy.py to /usr/lib/python2.4/site-packages
If you hit an error related to importing scapy.all, you just need to change the import to refer to scapy (not scapy.all). See examples in parse.py for example.