The standard disclaimer applies. The document is provided on an "as is" basis. The author provides no warranty whatsoever, either express or implied, regarding the work, including warranties with respect to its merchantability or fitness for any particular purpose. You can easily ruin your hard disk when trying to do something similar to what I am reporting here.
This is a kind of a field report about my (Bernhard Treutwein) experiences with Grub and other boot managers. Although it worked for me, there is some chance that it might ruin your system.
I succeeded to "chainload" from Grub into an El-Torito CD with the help of two tools from other boot-manager projects: memdisk (see: http://syslinux.zytor.com/memdisk.php) from the Syslinux project and sbm (see: http://btmgr.sourceforge.net/about.html) from the Smart Bootmanager project (sbm appears to be orphaned, and the maintainer of Syslinux seems to be a bit hostile to Grub).
If you need both (the usual disclaimer holds here: Use them completely on your own risk, be warned that you can ruin your hard disk with only some keystrokes. Do not blame me, if it does not work for you, I only report what I have done successfully) you can find here memdisk and a bare version of sbm.
This sbm image has only the following options left in its menu:
It defaults to booting from CD directly (without a delay, resp. with a delay of zero seconds). If you need to enter the menu you have to hold down the Ctrl key during loading sbm.
The menu entry for Chainloading an El Torito disk in my menu.lst file is:
title Boot "El Torito" CD with the help of memdisk/smart boot manager
kernel /boot/grub/memdisk.bin
initrd /boot/grub/sbootmgr.dsk
If there is no CD in the drive, sbm complains about a "Disk error! 0xAA" and if you hit any key, SBM enters its Boot menu. The same happens, if the directory of the CD is not yet loaded, or if the drive cannot read it (e.g. RW disk in an older drive), so it is worth while to retry loading the CD by hitting any key in response to the "Disk error! 0xAA" message and Enter on the (highlighted) CD-ROM line in SBMs Boot Menu.
With memdisk version 2.03 and later you can compress the disk image with gzip and memdisk transparently decompresses the image:
title Boot "El Torito" CD with the help of memdisk/smart boot manager
kernel /boot/grub/memdisk.bin
initrd /boot/grub/sbm.dsk.gz
I changed the options of the SBM image by creating a boot floppy with sbm and saving the changed settings to the floppy. Then I extracted the first 18k bytes from the floppy.
Special thanks to Paul Hedderly and A V Le Blanc for their postings on the Grub mailing list.
PS: You can also use PloP to achieve these goals, see my notes on PLoP
Bernhard Treutwein, 9. Aug. 2004, last changes: 4. August 2010
btreut (at) lrz (dot) uni-muenchen (dot) de