[CentOS] Reg. Kernel switching

Hi all,

I am a newbie to linux and this is my first mail to this group. We
have a PC running Centos version 2.6.9-42.0.2.EL. I needed
to load a router software called Nistnet and it would not run
properly. It is looking for RTC (Real Time clock) support as a
module.

I 've gone through the LKM Loadable Kernel module support under
Documentation pages of Linux.org and did the following:

located the kernel release:
uname -r
2.6.9-42.0.2.EL

next navigated to the /usr/src/kernels/2.6.9-42.0.2.EL-i686 (this is
where the kernel is located on this PC)
then issued a make menuconfig command

It took me to through the menu and under device drivers> character
device drivers i chose the Real time clock support as a module.

Then exited out of the menu and did make modules_install.
Then rebooted.

However, the PC while rebooting showed some messages like
fast_rtc: lost around 26 interrupts at 8192Hz.

this keeps on appearing on the screen for a while before reboot and
after the system reboots, I see that at boot time, the ethernet
interface does not come up.
It gives the follwoing error:
Device eth0 has a different MAC address than expected, ignoring.
Also i get the following error messages :

Cannot open  /lib/modules/2.6.9-42.0.2.EL/kernel/arch/i386/kernel/
microcode.ko no such file or directory
and cannot open
lib/modules/2.6.9-42.0.2.EL/kernel/drivers/net/sunrpc/sunrpc.ko no
such file or directory.

if I do an updatedb command and then slocate microcode.ko, I still see
it under this directory. However, if I navigate to the kernel
directory under 2.6.9-42.0.2.EL , there is nothing under it. If i
issue ls -al there are a totoal of 16 entries but I cant see them.

Can any one please tell me how to revert back to the original
configuration or to undo these changes? I have copied the config-2.6.9-42.0.-EL release from Centos site to the /boot thinking it would revert to the original default config. Then I rebooted the PC but I still get the error-Eth interface has a different MAC id than expected or unable to bring eth0 up.

So, at the boot time, I am currently choosing the kernel version 2.6.9-32-EL. With this I am able to browse the Internet. But I want to make the version 2.6.9-42-EL up. Please some one help me!!

Thanks,
Padmaja
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