It needs a bit of skill to installed an iso image recorded in a hard disk.
proves successful and is exactly what I have been doing with my new Suse 10.3, without burning into CD first.
The skill needed is to convert isolinux, which is the boot loader for CDs (majority), into Grub is used to boots from a hard disk.
Also some installer may insist on obtaining the files from a CD drive and thus the method is not always successful. I would say more than half of the iso I have tried can be booted from a hard disk, especially the Debian family like Ubuntu, Knoppix etc.