You need to edit your lilo.conf (lilo) or menu.lst (grub) files to specify the root partition that Linux will boot from. An option is passed to the kernel at boot which tells it which partition is your root partition. You need to edit this option as well as /etc/fstab.
I'm not sure which bootloader Ubuntu uses, but locate the configuration file (whichever one it is)...
...if it's lilo.conf, then change the line "root = /dev/sda1" to "root = /dev/hda1", rerun lilo, and try it.
...if it's menu.lst, then change the kernel option "root=/dev/sda1" to "root=/dev/hda1", and try it.
Make sure you change /etc/fstab as well so that all /dev/sda* devices are /dev/hda*.
That ought to work...