CentOS/RHEL have two challenges: they are very tied to Python 2.4 (and Scapy requires Python 2.5 for its latest version) and they require a kernel upgrade to use veth pairs for local platform testing.
If you only need to control eth interfaces for a remote platform, you can use CentOS/RHEL without major disruption. The key is to download scapy-1.2 from the following link:
wget http://hg.secdev.org/scapy/raw-file/v1.2.0.2/scapy.py
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.