most of the Live-CD or Live-DVD use a /boot-folder for the kernel and the initrd.
The whole system is inside an image, which will be mounted as a virtual harddisk
The first part of the boot process wil detect your hardware. This usually is a very complex process for all the imaginable pcs around.
Then the system and the system services will get started, which might be quite a number to start up depending on the DVD you are using.
The last step will be the desktop environment itself, which could be minimal like fluxbox etc. or huge like Gnome or KDE.
For the first part, the kernel and hardware part, you could hand some hints to the kernel mostly known as cheatcodes. They are numerous and are depending on the DVD you are using. Ask in the distribution's forum for those cheatcodes you can pass to the kernel to faster configure your system.
For the second and third part, i am afraid, you can only carefully search for distribution that just have the tools, software and services, you actually need.
Personal Note: Look for sidux.com
Fast booting Live-CDs for KDE/Fluxbox- and XFCE/Fluxbox-Desktops and DVD to have them all.
There could be an LXDE-Version in the future. Thats my personal taste and pure non-commercial advertisment, so be warned!