If your usb isn't working you would still be able to install debian via debootstrap. Simply install debootstrap and mount the debian partition as /mnt.
Next you can install the minimal debian to /mnt with
debootstrap squeeze /mnt http://ftp.debian.org/debian/
Now you can chroot into the new install to configure it (because this will be a bare minimal install) with
sudo chroot /mnt /bin/bash.
Now where gonna run the second stage of debootstrap with /debootstrap/debootstrap --second-stage this will install some more package like apt-get that you still have configure so thats next. Type in nano /etc/apt/sources.list and insert the right mirrors something like this will do:
# main system
deb http://ftp.debian.org/debian/ squeeze main contrib non-free
deb-src http://ftp.debian.org/debian/ squeeze main contrib non-free
deb http://security.debian.org/ squeeze/updates main contrib non-free
deb-src http://security.debian.org/ squeeze/updates main contrib non-free
Now you can begin installing some aditional package like a desktop and the kernel
apt-get install gnome gdm synaptic sudo linux-image-2.6-*ARCH linux-headers-2.6-*ARCH
where *ARCH is you put your cpu architecture, 686 for new 32 bit amd64 for 64 bit and 486 for older 32 bit pc's
If you install the 64bit kernel it would be smart to install the 32bit libraries to
apt-get install ia32-libs ia32-libs-gtk
Next you'll have to configure /etc/fstab to make sure all the partitions are mounted correctly on boot.
For this you will have to look up the right uuid's for the disks with gparted or blkid in the ubuntu install. Your fstab will probably look something like this:
# /etc/fstab: static file system information.
# Use 'blkid' to print the universally unique identifier for a
# device; this may be used with UUID= as a more robust way to name devices
# that works even if disks are added and removed. See fstab(5).
# <file system> <mount point> <type> <options> <dump> <pass>
proc /proc proc defaults 0 0
# / was on /dev/sda1 during installation
UUID=471aeebf-914c-4a5b-b376-3f254c6cffa9 / ext4 noatime,user_xattr,errors=remount-ro,barrier=0 0 1
# /home was on /dev/sda6 during installation
UUID=efac19df-63eb-4c4c-8470-0af09b9d6384 /home ext4 noatime,user_xattr,barrier=0 0 2
# swap was on /dev/sda5 during installation
UUID=28faae3c-c01e-45cb-8c25-9a49b22450c2 none swap sw 0 0
/dev/scd0 /media/cdrom1 udf,iso9660 user,noauto 0 0
Now you can make a new user for your new install with
Now you can exit the chrooted environment and run sudo update-grub in your ubuntu install to tell grub that there is a new install. Now your ready to boot into your new debian system!