to get the dual boot working again I had to enter:
title Ubuntu 7.10, kernel 2.6.22-14-generic
kernel /vmlinuz-2.6.22-14-generic root=UUID=e4af70f0-d555-49ab-8dd0-687cc3e7f81c ro iommu=noaperture quiet splash
in the /boot/grub/menu.lst of the Mint system.
I still don't know why the menu.lst was changed after the Mint upgrade?
Has anybody an idea, thought or answer?
I would like to declare the case as solved