I recently set my computer up as a dual boot system. Two drives on the same ide channel, hda is my main drive with fedora core 4, hdb a development drive with RH8. When I boot, I get an "Error 13: invalid or unsupported executable format" message. I tried changing the bios for the primary master drive to enable LBA, no help. Any ideas? Thanks in advance.

Just to clarify, did you have FC4 installed on hda first? Did it used to boot?

FC4 was on hda first and it booted okay. After I installed RH8 on hdb, it gave me the error.

I would use this to restore the FC4 GRUB which should still be working.

I would boot up with the FC4 cd#1 and type: linux rescue
After it is done detecting and what-not, type: grub to get to the grub prompt.
Then, you can tell grub to use FC4 grub.conf .....
Since I don't know what partition it is on, I would use find to show me the options.
For example:
grub > grub> find /sbin/init
(hd0,0)
(hd0,4)
(hd1,1)

My FC4 is on (hd1,1) so I'll use that next

grub> root (hd1,1)
Filesystem type is ext2fs, partition type 0x83

Now, I'll tell grub to use the MBR of hda

grub> setup (hd0)
Checking if "/boot/grub/stage1" exists... yes
Checking if "/boot/grub/stage2" exists... yes
Checking if "/boot/grub/e2fs_stage1_5" exists... yes
Running "embed /boot/grub/e2fs_stage1_5 (hd0)"... 15 sectors are embedded.
succeeded
Running "install /boot/grub/stage1 d (hd0) (hd0)1+15 p (hd1,1)/boot/grub/stage2 /boot/
grub/grub.conf"... succeeded
Done.

Now, you should be able to boot FC4. When you are booted into FC4, mount the partition where RH8 is loaded and go to the /boot partition and get the grub.conf info which you can copy over to the FC4 grub.conf

Thanks for the help, but I think I blew the mbr away. At the "checking" stages, I get "file not found" errors.
When I go to /mnt/sysimage/boot/grub, the files (stage1, stage2, etc) are there.

Can you show the results of fdisk -l

Also, just for kicks, will you run these commands:

Just to clarify; Do you want me to boot to Red Hat on the second and working drive, or boot to the
Fedora Core rescue mode and run the commands? Thanks for the help.

Never mind. The second drive was too small. Back to square one.