Booting from an ISO image on DVD

IBM Thinkpad 600X laptop. Currently running Win2000/Debian Linux dual boot. I want to install a Red Hat Linux distro on the whole hard disk. I thought I would be able to boot from an ISO image on DVD, but I'm not having much luck...

I burned a Red Hat Linux distro ISO image on to a DVD at work, using Nero.
I removed the CD drive from the Thinkpad and installed an IBM 6x DVD drive in the same caddy.
Then I configured the Thinkpad to boot up CD-HD1-Floppy sequence.
Result: On boot up, the DVD drive lights up first and the drive "rattles" as if it is going to load, but the boot sequence then goes on to the hard disk without loading the DVD ISO image.

Any tips? Does the Thinkpad need some drivers for this?
Thanks
Bruce

Just a thought....

Are you sure the existing O\S's on seperate partitions on your disk are not conflicting with your new O\S to be created? Why not try on a clean disk and ensure it is of the right file system, NTFS, FAT32, UFS or whatever it may require.