Implemting a packet filter for WinXP

I'd like to implement a packet filter for Windows XP.  I'd like my code to have access to both inbound and outbound traffic, including the ability to modify or drop packets.  For example, when a packet meeting certain criteria arrives, I'd like to be able to drop it, along with other packets from the same IP address.  I'd also like to be able to restrict outbound traffic through packet inspection.

I'm familiar with TPC/IP, how to decode packets, etc., so what I'm really looking for is a pointer to some sample code on how to hook into XP at a relatively low level.

Thanks,
Eric