You can try to boot UBCD from the external optical drive directly
Because you can boot from an USB floppy disk, you can try to put PLoP bootmanager on a floppy.
When you boot to PLoP, USB support is added to the BIOS (PLoP is a BIOS extender. Then you can boot from an USB stick when selecting USB in PLoP, so you can boot UBCD or another tool (like a small Linux distribution) from an USB stick.
For backing up data, you better use a small Linux distro like Puppy Linux, Slax, Parted Magic, ... They give you a nice graphical way to copy files you want to keep.
Download Ultimate Boot CD v5.0
Use Parted Magic
for handling all partitioning task: http://partedmagic.com/