I went into the rescue mode and:
Grub-install prompted that the installation was successful. I reboot the computer and it still boots to WinXP... However, just before WinXP start loading, I can see some text which looks like grub, bur only for a half second.
WinXP and RedHat are on the same hard drive and /boot/grub/grub.conf:
title Red Hat Linux (2.4.20-8)
kernel /vmlinuz-2.4.20-8 ro root=LABEL=/ hda=ide-scsi
I really appreciate your help,