I don't know if RedHat comes with a utility to update grub, I'm pretty sure Ubuntu has one called update-grub or something along those lines.
You can manually edit /boot/grub/menu.lst, however.
Perhaps there was a second hard drive in your first box, and none in your second box? That could cause your hard drive to no longer be hd(1,0) or whatever partition it was, and instead be hd(0,0), which would need to be changed in the bootloader.
You can try reinstalling grub, though, which I think would automatically configure the settings for you again, if you want to avoid editting the file yourself.
Who knows, maybe it has nothing to do with grub at all
Just trying to help troubleshoot.