If you are going to use the downloaded DVD ISO image on your pc itself, i suggest you use a
Daemon Tool such as
Alcohol 120%.
These tools set up a
virtual CD/DVD drive on your pc, where you can
mount/unmount various images.
However, if you are going to use it somewhere else, then you can probably extract the contents using
Isobuster, and then burn those contents into seperate CDs.
Another alternative would be to split the image, like you said, into different parts using a Splitter Software, burn them to CDs and later rejoin them to use them.
Search on
www.download.com for these softwares.
Savvy