Hello mate
Look like your question has been pretty much answered.
I use barry allen mentioned above to install more then one image on my 800 at any time. Barry Allen allows you to install images to removable media in the case of the 800 USB or hard drive. USB is preferred as you don't want your hard drive running all the time while you using a image.
Best multi-boot setup is the very latest CVS image in your 800 flash memory. Oozoon and Nabilo Pure flash are CVS images and can be updated over the internet meaning the drivers are always upto date.
Then i use barry allen to install and amount of images i like which is 8 in my case as i like to try support all images.
Use the guide above to install barry allen on any image not needed if you install pure flash or Oozoon.
Then use this guide to install images to work through barry allen
http://www.sat-universe.com/showthread.php?t=134942
Now reboot your 800 and you'll see the red barry allen splash screen where you can choose which image to use.
Ferret