title: How do I hook the TCP stack in Windows to sniff and modify packets?
body: <p>I'd like to write a packet sniffer and editor for Windows.  I want to able to see the contents of all packets entering and leaving my system and possibly modify them.  Any language is fine but I'd like it to run fast enough that it won't burden the system.</p>
  
  <p>I've read a little about WinPcap but the documentation claims that you can't use WinPcap to create a firewall because it can't drop packets.  What tools will help me write this software?</p>