(moved to Installation)
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If I understand you correctly, you've already got Grub installed on hdb not on the mbr. Since you'll be removing the existing mbr, you may be able to do this:
1. Boot off the 1st Fedora CD or use the Fedora Rescue CD
2. At the boot prompt type 'linux rescue'
3. The rescue mode will find the fedora installation
4. Type 'chroot /mnt/sysimage' (without quotes)
5. Type 'grub-install /dev/hda' (to install Grub to the MBR of the 1st HD - now the only drive)
6. Restart and you should get the boot menu
When the boot does occur, grub may still be thinking '(hd1,0)' rather than '(hd0,0)'. If that's the case, you can stop the boot at the menu and then use the 'e' (edit) to make that correction and see if it boots properly. If so, you'll have to use gedit to change the /boot/grub/grub.conf to make the change permanent.
Linux & Beer - That TOTALLY Computes!
Registered Linux User #362651
Don't use any of my solutions on working computers or near small children.