I had rhel4 along with Win XP in dual boot. Somehow, due to some problem with grub, on booting came the "grub>" prompt. I could boot in windows using the commands :
root (hd0,0)
makeactive
chainloader --force +1
boot

as mentioned in the thread Booting windows from the grub prompt.

My question is ---
while installing grub loader, a part of the loader is installed onto the MBR and the remaining (menu) part resides in the /boot/grub/grub.conf file. what happens exactly by executing the above mentioned commands on the "grub>" prompt?
a) Does it overwrite the MBR with that of windows? OR,
b) Does it simply tell the grub program "on the MBR" to always boot windows (same effect as having and entry only for windows in grub.conf file).

If (b) is right, then it means grub is still intact on the MBR. In case I want to reclaim linux partition, will it be fine with this, or I still have to write windows loader on the MBR?

No. It just point it to the partition where the windows bootloader is (hd0,0) to take over booting. It is a one time thing and doing it this way will mean you need to do it every time you boot windows. If you look at the command you entered, you can see it is only pointing to the partition of windows.

If you were booting from grub before and now have to use this method, I would expect that your mbr has problems. You don't give enough information about what happened for anyone to give a detailed answer.

Grub is still installed on the master boot record. All those commands do is tell grub to pass control to the partition containing Windows to continue the boot process. Installing the Windows loader will overwrite grub and make it harder to gain access to the Linux partition. You need to repair the grub configuration files and update grub with the repaired configuration. I do not know the exact procedure for RHEL4, but basically, you need to edit grub.conf and run update-grub. You may need to boot from a recovery disk for this to succeed.

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Thanks friends for your reply. Now that i have formatted the linux partition and executed the mentioned commands at "grub>" prompt, the box straightaway boots in windows. My query was aimed at the concept involving the grub's resident part on the MBR.
Thanks again for the response.