Hi you all,
I have been fighting a few days with a variant of the current problem, so I share it with you.

My aim is to boot from ISO the latest Knoppix version. This ISO hold on a usb 320 GB external disk with several partitions.

The only way I managed to boot Knoppix 6.4.3 from this disk (/dev/sdb) was to create a suitable size partition (/dev/sdb8 and then cat KNOPPIX_V6.4.3DVD-2010-21-20-EN.iso > /dev/sdb8

booting with gujin as bootloader it works fine.

However I don't want to waste a partition for KNOPPIX and I'd like to boot it straight from the ISO image.

my USB HDD has FAT (/dev/sdb2) NTFS (/dev/sdb3) ext2 (/dev/sdb6) partitions and I can place the ISO on anyone.

I made some attempts using GRUB2 (I can also boot from grub4dos) but unsuccessfully (basically the iso image is not found and the boot process drops to prompt)

this is grub.cfg entry

menuentry 'KNOPPIX' {
set root='(hd0,7)'
#loopback loop /KNOPPIX_V6.4.3DVD-2010-12-20-EN.iso
linux (hd0,6)/boot/isolinux/linux desktop=gnome bootfrom=/dev/sda7/boot/isolinux/*.iso config=scan home=scan ramdisk_size=100000 init=/etc/init lang=it vt.default_utf8=0 apm=power-off BOOT_IMAGE=KNOPPIX
video=vga16fboff nomce loglevel=1 tz=localtime
initrd (hd0,6)/boot/isolinux/minirt.gz
}
you can see I extracted linux and minirt.gz from the ISO and placed on /boot/isolinux in order to fire it

Anyone can help me ?

Thanks in advance
benny