It is possible to boot ESXi from a live CD but it probably isn't what you want. The ESXi installer is actually a version of ESXi booted from CD with a modified set of init scripts. The problem with running ESXi from a CD is that there is no place to store any configuration changes (licences, registered VMs, networking configuration, etc). When booted from a CD, ESXi will store those configuration changes in /tmp and will lose those changes on a subsequent reboot.
For the adventurous souls that just want to play with a liveCD version, if you know how to extract the dd image from the installer CD you have most of the pieces you need. Just look at the installer CD's isolinux.cfg file and in the list of modules replace ienviron.tgz by environ.tgz and remove install.tgz. Use the gz and tgz files from the dd image. Just remember that you won't be able to save any configuration changes so it won't be of much real use.
