I like to use Scapy with Python v2.7 under Windows 7.
The particular Python distribution I am using is Enthought Python distribution 7.02.
Intrusive update: please note that this answer is outdated, with recent versions (>=2.4.0) scapy will ONLY require Npcap (or Winpcap) to work, and IPython for the console. Have a look at the official windows page
In case someone needs Scapy for 64-bit + Python 2.7, I've uploaded the binaries here:
In addition, you probably need to install WinPcap from the official site
Compiling it yourself required a few fixes - I'll commit them upstream soon.