I want to create a multiboot DVD with Ubuntu, Kubuntu and Xubuntu Linux distros and on their install discs there are directories used by all 3 distros...I mean I cannot just copy the installation files of the three distros in one folder, because Ubuntu's files will get replaced with Kubuntu's and so on... How can I put the installation files of every distro in a separate directory on the DVD ?

I realize the previous post is 2 years old but it'd be a shame for it to go unanswered. I'm sure this information could help any other curious members as well.

Creating a multiboot CD containing multiple Linux distros is possible. I'm working on a multiboot CD containing the three distros you mentioned and I myself am having a few difficulties.

Anywho, this UbuntuForums.org post should help you ALOT.:
http://ubuntuforums.org/showthread.php?t=703905&page=3

Jotnar's post here is also very useful.