Which OS does not boot correctly when GRUB is installed in the MBR ?
Also, you can always use a Linux boot disk for the moment until GRUB is fixed.
Your WindowsXP install seems a little strange. What is on the FAT12 partition ?
Your GRUB entry for Windows XP should look like this:
title Windows XP
Also, for the RedHat 9 entry, usually there is a line for initrd
title RedHat 9
kernel /vmlinuz-2.4.20-8 ro root=/dev/hdb6
But once again, which OS does not boot correctly when GRUB is installed in the MBR ?