Hi
i have redhat EL desktop 4.6 version.For tftp i want to add rtl8102 nic drivers
in initrd.img, for redhat desktop. i am new one in linux so if somebody
write step by step configuration for extracting initrd , adding nic and make again initrd.img and vmlinuz.
Thanks for help

Why do you need it in the initrd ? ... the initrd is really only for loading drivers for the storage device

for tftp boot or pxe booting drivers must be add in initrd.img

Sorry for this RTFM answer, but look in the mkinitrd manpage for your system. On mine, there is the -m option to include modules.

On my SuSE installation:
I could simply add the module to this variable in this config file. However, your system may be different. The mkinitrd manpage is probably the best place to look.

There are two types of initrd files. One is a compressed ext2 filesystem. The other is a compressed cpio archive.
Here is an example of extracting the contents of the initrd file on my system:
mkdir ~/initrd
cd ~/initrd
cpio -vid < <( zcat /boot/initrd-2.6.31.5-0.1-desktop )

However, you still may have other things to edit such as /etc/modprobe.conf or a file in /etc/modprobe.d/.
It would be far easier to learn how to use mkinitrd on your system than inserting the module manually.