discarding packets using C#

would somebody plz let me know how i may be able to stop for
example SYN packets from reaching a certain IP address programatically using C#.
i m working on LAN and trying to build a firewall type
application which can block packets from the network.
actually i got a Dll from codeproject, but it blocks all the packets and
i am interested only in blocking SYN packets. m really
hanged up somebody plz help me out.
m using C# (.net 1.1) on Windows 2000.
[489 byte] By [suezkhan] at [2007-11-19 18:28:03]