I believe this thread belongs to Linux - Newbie forum since it's not related to a specific software.
Anyway, to install previously not-installed packages you don't have to boot into the Live CD. Just pop the CD in the tray while you are in Ubuntu. Then start Synaptic package manager (System > Administration > Synaptic Package Manager) or any other software installation tool available. (Ubuntu have one their own "Add/Remove Applications" program Applications > Add/Remove...)
Then you'll be able to install whatever you need, because as far as I know in Ubuntu 8.04, the installation CD is automatically added to the repository list.