hi;
Simon:
Now please suggest, whether assembly is a good idea to write down the TCP/IP stack ????
Dan:
Plus, the vast majority of TCP/IP source code you will find (and may be able to exploit) is written in C.

i agree with dan. when it comes to faster development C may be a way to go.
however i feel atleast for checksum computations in IP layer assembly should be used.if you are using C for remaining code you can use inline assembly features.

regards
pranav