ethernet + 8051:
http://www.8052.com/ -- http://www.8052.com/tcpip/
http://www.cornelius-consult.de/int/intethernet-embedded.html
http://web51.hw-server.com/descript.html
http://www.circuitcellar.com/library/print/0902/brady/

ethernet + microcontroladores:
http://www.beyondlogic.org/etherip/ip.htm

pic + rtl8019as + ISA:
http://elserver.forknet-ar.org/harpo/uch/seminario/

bus ISA:
http://www.techfest.com/hardware/bus/isa.htm
http://www.interfacebus.com/Design_Connector_PCAT.html

uIP:
http://www.sics.se/~adam/uip/

UDP/IP Checksum:
http://www.netfor2.com/checksum.html
http://www.erg.abdn.ac.uk/users/gorry/course/inet-pages/ip-cksum.html