GNU GRUB version 0.97 (639k lower / 1039336k upper memory)
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That sounds like grub error 7: quoting from the grub legacy manual:
7 : Loading below 1MB is not supported
This error is returned if the lowest address in a kernel is below the 1MB boundary. The Linux zImage format is a special case and can be handled since it has a fixed loading address and maximum size.
In your last session before the error occurred, did you do any partition resizing or configuration changes, especially to the grub config file /boot/grub/menu.lst (or possibly /boot/grub/grub.cfg in Red Hat family Linuxs)?
The only suggestion I can make is to try your install cd. Does is work as a liveCD also? If so, try booting the liveCD. When you get to the menu, look for an option to boot from the hard drive. If there is one, you may be able to boot into CentOS. Once there, try removing then re-installing grub. Or, better yet, remove grub and install grub2.
The problem you have is in grub itself. Upgrading to grub2 should fix that problem.