A DESKTOP ISO will _NOT_ work!
o) Now, it's a blatant lie that you would not need an Internet connection. You got to have it; if not, go and do something else.
o) Okay, once you got you alternate ISO image ready, do the following:
sudo mkdir -p /media/cdrom sudo mount -o loop ~/Desktop/ubuntu-10.10-alternate-i386.iso /media/cdrom
gksu "sh /media/cdrom/cdromupgrade"
o) Yup! that's pretty much you need to do.