I had installed the debain sarge and wanna use static ip that means converting dhcp to static ip.

DEBIAN SARGE converting dhcp to static ip
free:~# vi /etc/network/interfaces
replace "dhcp" to "static"
add this lines address 10.6.81.163
netmask 255.255.255.0
broadcast 10.6.81.255
gateway 10.6.81.1
and
free:~#ifdown eth0
free:~#ifup eth0
everything is ok. now it is working with the lovely static ip :)