Multiple boot from USB stick

[Karsten Malcher]

Hello,

i want to setup an USB stick that is able to boot different OS form ISO.
But all examples i could found does end in errors like "error: no such 
partition".

Can i find anywhere examples to boot an ISO with grub 2.02.
I don't understand the general structure how to specify the iso file on the 
stick and initiate the loop to read and boot it?

My most recent problem is to boot an freedos image to make an BIOS update.
When i look at the documentation there is no real hint how to do that?
http://www.gnu.org/software/grub/manual/grub.html#DOS_002fWindows

An very special problem is to boot an iso image with an freedos in it that has 
an bios updater.

Can you help me please?

Best regards
Karsten