firewall configuration!

hi guys

is this possible for firewall configuration .. my requirement is like
following way..

1) i want to particular ip on particular subnet mask
2) also want to block particular port on that particular ip
with
subnet mask..

I have fc4 and i want to implement this c program on different linux
version.

is this possible to change without iptables. if yes then how/if no then

how can i deny access to particular ip on particular subnet mark with

given port, and i want to do this all with C program, if is there any
function then plz suggest me.. or help me, how to write program if
there is no any specific function.

Chandrakant