adding default gateway and aditional gateway
 

please answer my question........
I want to add default gateway and aditional dns valu to my lan card. can any one send commands for this kind of task.....?

You need to tell us which Distribution (e.g. RedHat, Fedora, Ubuntu, Suse, Slackware) of Linux you're running and which version of that distribution.

Also your question about DNS is a bit confusing. Are you trying to use DHCP and populate /etc/resolv.conf automatically?

In general though:
You can add default route in the network configuration file or the configuration file of the first NIC. You can add additional routes at command line with "route add" command or make them permanent by adding a new route file associated with the NIC the route applies to to be started at the same time the NIC is.